Like Mal - I too sell kitties on the Market Place. I have over 400 good quality kitties that I place there (often with the latest traits), simply because placing 400+ kitties inworld would be unviable! I dont often have any problems with the sales. IF (at all) there is a problem, I will offer a full refund or a replacement kitty.
I believe, that breeder who take their reputations seriously, will not offer dud kitties, either inworld or in the market place.
But each to their own - if kitties are available both inworld and in the market place, it offers people a greater range of choice and they can choose whatever is the most convenient way for them to shop.
That's my penny's worth!
P.S. I intend to continue offering my best kitties both inworld and on the market place. If anyone has a problem - they only need to IM me!