My players want to start a business on Nar Shaddaa so they can make more money during downtime. They've accepted that the normal cargo/smuggling runs they do in between sessions only break even due to expenses like routine maintenance, fuel, customs, bribes, etc. But still, even with this hint, they want to try to run a cantina in their off time.

So I can do this a couple ways. First, they're nominally working for a Hutt already. So I could have him take a percentage of the business. Second, I could have the local swoop gang charge them for protection. The gang is already known to be the equivalent of local law enforcement and DPW (they clean up corpses, or force others to do so anyway). Third, I could of course simply have their cantina constantly trashed, robbed, torched, and other nasty things somewhat common on Nar Shaddaa.

And there's always the very realistic issue that the market for cantinas in the area is somewhat full so even without hostile action against them, the cantina might not make enough money to survive.

I like the idea of them having a base in addition to their ship. I also like the idea of yet another money sink for their hard-won credits. So I don't want to push them away from the idea but I really don't want them to be able to get rich off it. The rules for homesteads cover legit businesses on relatively lawful worlds. But we're on Nar Shaddaa...

Well, the Catholic Church took 10% in “tithes”. I would think that 20% could be really painful, but not quite painful enough to make the targets band together and wipe out the thugs.

I would not hammer them too much, I understand your reasons and agree largely but hit them too hard and you either have them give up on the endeavour or they decide to deal with the issues (ala swoop gang) themselves. I would use one of the first two with the third being the end result if they refuse to pay whichever of the first two you chose to use.

As to profit or loss I would suggest you make it a dice roll based on the cantina's 'stats', with a difficulty based on the location. So for example a base attributes for a cantina might be building 2 (an average cantina) with the skill alcohol 3 (above average drink). If the cantina is in a good location on Nar Shadaa (near a spaceport area or somewhere else that should get good passing trade then have the difficulty easy, ramp up the difficulty the further it is from a good location. If they haven't paid the local protection racket/hutt then upgrade the difficulty appropriately. Then assign a credit value to success (plus how much each additional success is worth), with advantage and triumph giving benefits and threat and despair giving them problems. So for example lets say they roll for their cantina which is in an o.k. area and they have paid their protection money, they roll two yellow and one green with two purple and get 3 successes and 2 threat. This could mean that their cantina has made a profit of fifteen hundred credits (each success being worth 500), but they have attracted a bad crowd and so subsequent checks suffer two setback dice unless they clean up their place.

This is just an example but you get the idea, obviously the value of each success of failure would be up to you and your players expectations and the effect of advantage, threat, triumph and despair could be any number of things. I haven't read through the homestead rules so this is just something I threw together as a base idea.

@bradknowles: Though I agree in principle, there is a difference between Npc's/real world and Pc's. I know groups who would bridle at 5% and based off of that go out and take out the gang to save having to pay 20 credits. Whilst this does give the GM material to build adventures off of, including the fallout of such an action, it does also mean you should be aware of your groups likely response and try to avoid relying on them just 'sucking it up and paying'.

If I were a mighty Hutt and a group of ne'er-do-wells with no clout whatsoever wanted to do business on my turf, I'd take as much from them as possible, so that they just barely could make it with the rest. So, where there are no fixed tax rates, it all depends on the margin of profit.

As a GM I'd first consider how much I want my PCs to earn outside of adventuring, and then I'd have the rest taken by the landlord; trying to make them grumble without frustrating them.