I believe this to be a fairly simple idea. A confirmation screen on setting a pet up for sale and breeding.If you have a pet set to 'breed to/ sell to' -User Id #- there should be a confirmation screen saying not only the user but also thier Id number.
It could look like either "Are you sure you'd like to Sell this pet to -Username ,Id #-." and "Are you sure you'd like to set up Breeding for -Username, Id#-" It would be the same message with out the user Id number if none is put in.
I think this would help users who accidently set up thier pets for sale when they mean to breed,and vice versa.I also think it would help if you put someone's id number wrong or on accident.

Too many confirmation windows already. I feel this would be extra painful for those who test pets for free. Sorry, don't support. :(

I have to agree with Tap - there's no reason someone can't take extra care manually checking to make sure they've entered numbers correctly. The fewer popup confirmations the better in my eyes, I'd be delighted with less of them on the site, not more haha.