I wouldn't bother waiting for 4 confirmations unless the transaction was in a four-digit range or higher (if it was a 5-digit or higher one maybe you should wait for 6 confirmations).
I'm not sure about 0-conf transactions but 1-conf should be enough for anything below $500-1k (so most PoS transactions).
You should first ask yourself a few questions:
Who is able to do double-spends?
If they are, how much would it cost them?
Good points. I suppose I wanted to isolate my merchants as much as possible from being defrauded. I mean, if someone
does double spend then it's not only going to hurt the merchant but it's going to hurt my software's reputation.
I spent a good part of today reading up on how Bitcoin works though and I see how difficult double spending really is. I'd doubt someone would was that much time and effort just to buy a hot dog or something under $1K. Your points are well taken.
Thanks for the input!