Selling: great, valueable cel which'd make me 
rich gets heavily damaged, not worth a fuck 
anymore...

Collecting: cat pees on it...

Buying: getting outbid by someone who already has 
MANY of that type (EG Mss Lulu) and keeps buying 
like a friggen nerd... *hint* or mad dog 
collectors who simply buy whatever they get while 
others would cry of joy to get it...

Painting: screwups, paint unevennesses,...