What to look for?
Some basic advice for buying Bonsai trees:
Buy a tree that is suitable for the place where you intend to put it; only indoor (sub-tropical) trees will do well indoors, just like outdoor trees will only do well when placed outside (check the list of recommendable species below)
With techniques like pruning and wiring you’ll be able to change the shape of the plant somewhat, but usually the trunk and the root flare (nebari) are fixed. When purchasing a tree make sure you select a tree with a trunk that appeals to you.