Smart players (or devious GM's) should also think about the implications.
Remember real-world legality - in most countries, if you find something that might possibly belong to someone else, you have to report your find to the police. If you don't, and take it, it's theft.
If the owner can be determined, the found thing is returned, and in most countries a finder's fee can be demanded.
If noone comes forward to claim the found object, it will probably be auctioned off by the authorities - usually in such cases no finder's fee applies.
If you do take it, you can never know if some day the police will show up to have words with you about that thing (for example, the guy who found a necklace and just gave it to his girlfriend got in trouble when she brought it to the jeweler to fix the catch, and it was recognized from the description of stolen goods, and he then had to explain to a judge that he just wasn't thinking and didn't really mean to commit a crime... etc. Once in a while you hear about things like that)
Soo - if you find a car in a ditch next to the road, with the driver dead in it, what would happen if you just hid the corpse and took the car for your own? The drivers wife (or whatever) would report him and the car missing, sooner or later a cop would check the license plates, note that car is listed "missing" and stop you to check you out. And as soon as he sees your ID he'll notice you arent the driver who's also missing, and suspect the worst. - Similar in B5.
For example, if a ship disappears in space, and some time later a group of people show up in possession of said (still registered to it's previous owners) ship, well, piracy comes to mind... and as soon as they dock at some government station where someone can and will check their ship's registry, the players will certainly be arrested (possession of a stolen spaceship, suspicion of piracy and murder).
And that's only the authorities - you can never know who else might come after you because they think you might be the one who is responsible for the ship's disappereance ("hey, Don Machelli, our missing courier showed up again... but without our people and without our goods..." "Is dat so? Ju know wad to do, si? Find de ones hu did id...") Several movies come to mind here that could be used as inspiration...
Of course, there are things some "morally challenged" players can do to avoid at least the official entaglements... docking on certain space stations where noone would bother to check their ship's ID... and eventually get a forged ID (I assume that would mean getting 1; a new ship ID beacon to fix the problem of a casual scan by a passing warship, 2; forged ship registry documents to show a boarding party, and once you can afford it - 3; paying a lot of money to some corrupt government official somewhere in known space to have him enter your newly installed beacon signal into the registry database of his government to fix the problem of getting caught when docking to a governmant space station where they have the means to validate your becaon's authenticity - non-forged ship documents included)...
That would fix the basic problems of having a stolen ship, though on a very good search some inspector might note hull and engine numbers (or the fact that someone filed them off, which in itself is suspicious enough to warrant a forensic scan which would again turn up the real identity of your ship). Also a determined database expert might follow the history of your ship and again find something suspicious enough to crack your false ID...
Another possibility is selling the salvaged ship (whole or in parts) off to someone who doesn't ask questions. Look at the car example above to get an idea of the possible snags with this one - if you sell it to would-be pirates, and they get caught, guess who they'll rat out as their ship dealer? Same for "used equipment dealers" - if they get in trouble with the law over this, they will most likely squeal on you.
Government R&D sections on the other hand are pretty safe - IF they are interested in your find. After all, they certainly won't tell anyone the truth, and deny everything on general principles. But that's only for official trouble again - inofficial trouble might not bother with evidence when they can bribe the right official for proof...
But all that's assuming noone sees you doing the salvage - if at any point you are caught by a government ship trying to salvage a derelict vessel without having notified the government - well, as with the car example above, you would have some explaining to do. Or some bribing, especially in centauri space (size of the bribe dependent on how important the salvaged ship is - a centauri patrol captain will be happy to look the other way for a small gift if it's a wrecked old scow, but if it was a modern centauri warship it would probably cost you more than you could afford - or gain from the salvage. And in that case, you might have to pay a hefty bribe just so he'll forget your faces when reporting "his" discovery of the lost vessel)
On the other hand, if the players report their finding of said ship as soon as they find it, the authorities will certainly investigate. And if they (or the players) find enough evidence to reconstruct that the players weren't the ones responsible for the demise of it's former crew, then they will see the ship goes to the inheritors of the owners. In that case, a "finders fee" could be claimed by the players.
Depending on the total value of the ship in question, and the government involved (and the GM's wishes) from 10% to 1% (the bigger and more valuable the ship, the less percentage you'll get).
Alternately (especially if the owners are still around - for example when the ship is owned by a corporation or government organization) the reward for recovering it won't be percentage, but a fixed "salvage fee", reimbusement for their troubles. GM's decision (for now...)
And taxes... well certainly! Most governments will be happy to tax whatever they can (and so give an GM more of a chance to lower the players income from salvage)
Hmmm... maybe some guy at Mongoose should think about a small article in S&P about salvage rights for all the different alien governments... (BtW, if it's a Llort ship, it's "finders, keepers"... but you have to expect some kin of the former ship owner coming after you to try and steal it back!)