Has anyone ever sold a dog or any other animal and regretted it afterwards.

Yesterday I sold a guinea pig to someone, she has previously bought from me and I vetted her the first time around three years ago,(even though I breed guinea pigs I still care about where they go) so I was happy to sell her another one.

Now Im starting to worry that I made the wrong decision on the odd comment her son made.
I know there is nothing I can do about it now, but it doesnt stop me from feeling worried and guilty.

I've sold a fair few mice and a couple rats in my time, and I always, always worried about them afterwards - still do, really, even though the people checked out well - it's only natural I think, when you've cared for them.  If she's been good in the past, I'd try not to worry - you sound like you've done the most thorough check-up on her you could before you gave the the little pig, it's the best you can do.

Reassure yourself that you're doing a much better job than many breeders do :)