I guess I'll start out with the questions and explain later.

1) If you have a game cartridge (e.g. NES, N64, GBA, etc.) and the game loads properly when the system is on, does this mean that the entire game works?  That's probably a stupid question, but I know that disc-based games can load just fine initially only to freeze later on in the game due to scratches. 

2) Say I have a game cartridge but I don't have the system.  Is there any way to visibly inspect the cartridge to determine if the game works?  I'm somehow guessing not.

3) For those of you who have PSPs, if the actual disc is not scratched but the plastic UMD case thingie covering it is, does that affect playback? 

4) On an somewhat related note, how sensitive are Xbox, Xbox360, PSP, and Gamecube systems in terms of reading scratched discs?  In other words, will minor scuff marks prevent or interfere with playback or are the systems fairly tolerant of scratches like the PSX and the PS2?  This is probably going to vary a bit depending on experience, but any advice would help.

5) How long are those batteries in the NES cartridges typically good for? 

Okay, now the reason why I'm interested in this all of a sudden is because I won a metric ton worth of games (at least, that's what it feels like) last month at a postal auction.  I have a little bit of everything in terms of systems and genres, and while I want to make sure that all of these games work, I don't own some of these systems and/or I'm not that familiar with them (hence questions 2-5).  For the systems that I do own, I really don't want to have to go through each game in their entirety (hence the first question). 

I'm also trying to figure out whether I should start offering a return policy or just sell the items as-is, particularly for those items that I cannot test myself.  Any suggestions?

If a cartridge will load up, that's the only time efficient way to test.  There could be a ROM defect at the very end of the game, there could not be.  If the game plays, it's unlikely.  Whether or not a disc game is too scratched depends on the condition of the laser.  If it's dirty, it will have a lower tolerance for disc defects/damage/filth.  For games in cases, I don't think it should matter if the caddy is scratched.  The whole purpose is to protect the disc, and as long as the game plays, I don't think it's an issue.  CD-ROMs used to have cases like that too.  A lot of the time, I read that cell batteries often have a life of 10 years or so, but of course it can vary.

I'd recommend you test each game briefly, and sell them as-is, stating they have been successfully tried.  If you offer a warranty, I think you'll get taken advantage of.

At most I would load up all the games and make sure they load and inspect for visual damage.  Just put a disclaimer in your auction or where you're selling them that you're selling them as is and that you're not responsible for them given where you got them from. 

~jb

You should make a list of all of the stuff and put it up in the Marketplace so you can give us first dibs. ^_~

but yeah.. there's no way to tell if cart games work or not solely based on visual inspection.

Once I get the stuff somewhat organized, I'll do that.  ^^

I've had CD games screw up later in the game because of a minor scratch, but I've never had a cartridge with that defect. And I own some cartridges that look like they've been beat to hell and back (some even have the plastic in the back knocked out partially). Considering what you have to do to a cart to mess it up, I'd say they should be fine. GB games though, seem to mess up easier (I've bought used ones that don't work for anything...unless there was a bum run of both Pac Man and Super Mario Land carts I don't know about), but I've never had that issue with GBA ones.

Hope that helps somewhat.

Regarding question 1, many years ago I had a copy of Final Fantasy which had been damaged by someone dropping a beach ball on top of the NES while I was playing. You'd think that wouldn't do much, but it did. Anyway, you could play it just fine for a while, but every few days it would spontaneously reset and delete the saved data.

That's probably not relevant to your situation, though, since I assume you're not planning on playing each game for a few days.