sometimes right after a crested drops its tail it is a little off balance since it is used to having the weight of its tail behind it all the time. it usually takes a few days to adjust and then they are good to go. that is the only thing that really affects them as far as not having a tail goes.

you might pay less for a tailless gecko or you might not. not having a tail doesn't make the gecko any less valuable as it is common and really only an asthetic issue.

cresteds are hardy geckos and don't generally have many health issues. look for a gecko with bright eyes, a clean vent area, no signs of dehydration (a dehydrated gecko will have sunken eyes, be lethargic and its skin doesn't quickly go back to normal if you pinch it up a bit) and one that is being fed on t-rex crested gecko diet.