One of the problems with CRPGs is that it takes a very
careful design to make them
fun without allowing too much
munchkinism. Unlike the
traditional face-to-face RPG, you can't
change the rules in the middle of the game in reaction to such
abuses.
For instance, if there's some easy way to make money within the game, people with nothing better to do will go do it six zillion times, and end up with way more money than they are expected to be able to generate. Designers had better make sure players can't sell something for more than they can buy it for, or else that there's a limited amount of such stuff, or that the prices will change if they buy/sell a lot, or else you'll just end up with these moneybags players who effectively broke the bank. Same goes for any other commodity which can be exchanged for useful stuff within the game.
A classic abuse of this type was polypiling in Nethack. Collect all the useless junk you don't want into a pile, then zap the pile with a wand of polymorph. Presto! You now have a huge pile of other random items. You're likely to get some other source of polymorph or way to recharge the wand out of the deal if the pile is large, so it really is an infinite method. Later versions of Nethack fixed it so that polypiling doesn't work so well, while still allowing small numbers of items to polymorph reasonably.
This problem gets even worse in MMORPGs since there is direct interaction between the munchkins and players who are trying to have fun. Although at least in these situations the admins can step in and change the rules.