Two things I would like about RT are making money, lots and lots of money (take that Underpants Gnomes ), and getting to potentially deal with some of the xenos races in a less murder-death-kill manner, if one chooses to. To that end, if I were to want to make a character, what base job is best? Here is the brief run down:

Gavin is a man from the Calixus region, probably a hive world, like Scintilla; a place where the division between the haves and the have nots is very plain, and maybe the force of the oppression leveled by the Imperium, even way out on the frontier. After growing up as a have not, Gavin finally got a chance to leave his homeworld, and travel abroad, working for some less than ideal employers, but found that much of the Imperium was the same. He wondered how such a body had made it so far, and began to study some of the other races , those the Imperium had crushed, and those it still lived among. Out in the Expanse, these races were a bit more common, and he could see them, "study" them, and talk to them, if he felt bold enough. This practice led him to become a Xenographer, and his race of focus was the Eldar. While they were often vague and aloof, repeat attempts got him some information from them, after they sensed his desire was more scholarly (sort of how the high are pleased when their lesser charges take an interest in their betters). He was able to make friends, as much as anyone really can, with some Eldar, mostly corsairs, and the occasional Kaelorite, and found that, in principle, he liked them a bit more than the Imperium. Still, he had to live here, and deal with Imperials, so he opened a business, selling and manufacturing weapons. If asked about their own weapons, his Eldar contacts remained tight-lipped, but polite, until Gavin found out that some few Eldar, if properly enticed, will part with these marvels. A prospective buyer wanted some Eldar weapons, and had something to pay for them, a bag of spirit stones. Gavin found that, unexpectedly, his Eldar contacts were interested in trading some of their "simpler" weapons for such things. (As a dying race, the Eldar are finding themselves with a surplus of weapons they can't use, and even they need stuff.) This is when Gavin became a Cold Trade Broker. As a merchant, he still sells "regular" weapons, but for the right price, he can acquire rare Eldar equipment, and the Eldar won't even come looking for it.

So, you got through that crap. I want Gavin to have Xenographer (Into the Storm) and Cold Trade Broker (Hostile Acquisitions). He could easily find work with Rogue Traders of a more mercantile bent, or even just those who like to know people that know people. The two alternates do sort of repeat each other, but that's fine; they each say their won bit for who he is. He is a secretive salesman, aware of what his activities could bring down upon him, but willing to risk it. He might be able to sneak a bomb on a ship, so that his clients don't immediately turn him in, if they are more law-abiding, or sneaking their purchases aboard, to dodge witnesses of seeing "suspicious" cargo, and he has some connections among the Eldar. What base class would be a good choice for a gun-selling, xenos-consorting merchant? When would be the most lucrative time for him to grab them? I sort of thought Seneshal, but they get many of the same benefits early, so the alternates have less to offer.

As an aside, I know that RT characters make acquisitions for stuff, and get that stuff with their checks. How does a character with such a background act out SELLING stuff, either for themselves, or as a job done for their master (sort of how RTs make trade arrangements), and how do they make money doing it? On their scale, I doubt they will raise the PF much, if any, but in a game with limited uses of Acquisition, spending cash, for small, simple purchases could be relevant, and merchants do make money. Any help would be greatly appreciated.

You could make commerce checks during an active Endevour to add some amount of Achievement Points. For small stuff, 1 or 2 per DoS, for decent stuff 5 or so per DoS and for the good stuff, 10 AP per DoS.

As class I would suggest playing either the RT or the Seneshall. Though any class could work if you keep things on a small scale. Trading those items can be done in a variety of ways. The most obvious one is to turn it into a regular endeavor, where the goal is to make a lot of money by trading with these highly illegal goods. Check out the books for creating an endeavor.

Alternatively you can make this a part of another endeavor. In this case you trade things on a much smaller scale, not enough to make a ton of money but enough to help you make a profit on the endeavor you are involved with right now. Just as ship components can give a bonus to the points you need to complete an endeavor. Making a succesfull trade could give you for example +100 points needed to complete the endeavor.

Finally, you can trade individual items for personal favors and goods. You could for example, bribe some officals with genuine fashionable gadgets to make them look another way. Thus helping you on your current endeavor. Or you could talk to a collector and exchange a couple of those Eldar weaponry for that bauble you wanted to have. This could give a bonus on the aquisation roll or even foregoing by it totally.

Of course, every time you trade, you are taking a risk. The Inquisition who wants to know who are providing these heretical items, fellow cold trade competitors who dislike a free market, Xenos doing their engimatic thing when they suddenly decide for no apparent good reason to alter the deal, nervous buyers who prefer to stay anonymous and silence the guy providng the goods and ast but not least Corruption and Insanity because there is a good reason for man to say no to Xenos influence.

Well, as he is more "street level", I think I'd envision the Seneshal, over the Rogue Trader; he's a sneaky scoundrel and secrets-merchant, more than a leader of men. I could see him working for a Rogue Trader, like one of their on-planet contacts or resources, like most any Seneshal does, or perhaps being their xeno-contact consul., but he's more about the selling/acquiring. I envision him as a merchant, owning his own storefront, or being meetable in certain circumstances. He would sell numerous "mundane" weapons and armor, and maybe the occasional "special item" he found in a ruin (this would be archeotech-like stuff). If he "really knows you", or you were recommended to him, he might even sell you rare xenotech, likely something he traded from the Eldar. His usual modus operandi is "you bring something the supplier wants (usually spirit stones), and I will get that to them, and bring back some awesome weapons." For his purposes, the Eldar will do much to get back their lost brethren, even selling some of their quickly becoming surplus weaponry.

I have to confess that I haven't looked at the Endeavor system much, so some of that bit goes over my head. I'll read it over, and hopefully it will then make sense. Hopefully, having Good Rep (Eldar) [ spendy EA] and Peer (Kroot) will help him in such things, when getting gear or mercenaries arranged for his clients, especially when he has to deal with Rival (Inquisition), and all that entails.

So, as an NPC, he'll probably break down as a Seneshal build, with CTB and Xenographer, and just the littlest hint of Psy, you know, to give the inquisition one more little reason to care. He might mix some of my favorite Human items with a few "exotic" ones that your average Human would never have, thanks to his Eldar friends. Granted, much of it won't matter, if he's NPCing, as combat won't likely occur, and would go a bit beyond what a PC is likely able to find, but oh well, that's the joy of an NPC.

One last little thing. This is going to sound a bit dumb, but I'll risk it. I know that the Acquisition mechanics are the way they are for a reason, and one of the reasons that xenotech is always so rare is just that they don't encounter xenos that often. Is there a way a character who fits the Cold Trade niche could get something that lowers the Rarity a step (from being Extremely Rare to Near Unique down to Very Rare to Extremely Rare), or something, to represent that they actively acquire stuff from aliens, legitimately, and see them considerably more frequently. I suppose I could say that having Peer/GR (Xenos here) would give you your bonus to your Barter, Commerce, or Inquiry tests vs said Xenos, especially the Commerce tests, and that could increase their PF, where other Rogue Traders wouldn't have the same bonus.