According to the EotE Core book, you use the Negotiation skill to find non-restricted items to buy, and the Streetwise or Underworld skill to find restricted items to buy.

You also use the Negotiation skill to alter the price of the item.

My question is, if you are searching for a non-restricted item to buy, do you make 2 Negotiation rolls or 1 roll? I was doing 2 rolls, 1 to find it, 1 to alter the price. Maybe I should just roll it into 1 roll?

Two rolls. The game is about rolling dem bones

Couldn't you do it from the same roll? Successes are helping you find the item (with Failures canceling these out). Advantages/Triumphs would make the price cheaper while Threat or Despair could either raise the price or be used to bring something else about. I state this last bit, because sometimes I want something else to happen while the Players are trying to find equipment and don't always use it for making the items more expensive.

In general, if you can accomplish a task just as easily by making one roll as two, just make the single roll.

However...

The Negotiation roll to find the item uses a fixed difficulty, based upon rarity. The Negotiation roll to actually haggle on the price is opposed by the seller's Negotiation or Cool. So, in this case, I would have to make two separate rolls, one to find the item based on rarity, and the other to determine the price, get or give concessions, etc., from the vendor, assuming the item has been found.

Where does it discuss buying and selling anyway?

It's discussed a bit in the Rarity section of "Gear and Equipment", and in the Negotiation skill description in the "Skills" chapter.

Generally, I do it in one roll. Successes determine whether they find the item (and sometimes determines how many they find in the case of grenades, ammo or low rarity items). Advantage and Threat then alter the price. Triumph and Despair make things more interesting with either the vendor having access to some more "specialized equipment" the PCs may be interested in (basically offering them a chance to find another item instantly..but at the base cost) or if the item is particularly hot or would be of concern they gain the attention of local authority or even are interrupted mid deal by a sting operation or some other potential plot hook...in a future adventure I plan on having some ruffians mess up the store looking for the weekly protection money, setting up my group for an A-Team style episode.

Its all about that narrative dice man. However...Ogg has a good point that technically the haggle should be done against the vendors negotiation and not the set cost for rarity, but then that requires two rolls and then deciding how to spend advantage, threat, triumph and despair on them respectively, it also takes more time.

One possibly way of doing it is have the base difficulty set by rarity, and then either the vendors presence or negotiation (whichever is higher) upgrades said check or adds setback dice...however you then run the risk of affecting if they can buy it. I mean they may be able to FIND a vendor WITH the item...but maybe that item is being reserved for someone else and so they either have to offer a better price or even attempt to steal it later that night (if they are that desperate).

Sometimes context can matter and change the circumstances of the roll.

One roll for me. If the merchant would be harder to haggle with, upgrade some dice.

Doing the same thing twice, meh to that.

Ogg makes a strong case, and one I had not put much thought in. I read it earlier, nearly responded but then thought on it for a while. I am now converted.

I doubt I would go to the effort for minor or common items, but for anything involving rarity, I can only say I have been doing it wrong... and I'm glad I read this thread.

In general, if you can accomplish a task just as easily by making one roll as two, just make the single roll.

However...

The Negotiation roll to find the item uses a fixed difficulty, based upon rarity. The Negotiation roll to actually haggle on the price is opposed by the seller's Negotiation or Cool. So, in this case, I would have to make two separate rolls, one to find the item based on rarity, and the other to determine the price, get or give concessions, etc., from the vendor, assuming the item has been found.

I float by on this perception as well. My interpretation is:

The first Negotiate roll is required and opposed by the difficulty of the item rarity. This determines not only the availability of the product, but also its condition and reliability.

If an item is successfully located, a second optional Negotiate roll (if the players want to attempt it) is performed and opposed by the seller's Negotiation/Cool and determines the final/adjusted price from the base cost listed in the CRB.