[fencepost]

If the client is posting there because they're cheap and are going to nickel and dime and second-guess every decision then they may not be worthwhile (possibly unless you factor in billing for your time discussing every. little. thing. with them).

If they're posting there because they don't know where to hire someone to do contract work for them then you may well be able to work with them - particularly if you're personable and willing to spend some time handholding and making them comfortable. For that matter, if they've done something on one of those places and been burned by poor quality, poor understanding, language issues, whatever then it may make them more likely to work with you if you don't have the same problems.

It's a question of making sure there are realistic expectations on both sides. If a client is going to need concierge service beyond the raw design and coding and you're able to provide (and get paid for) that then you may be in a good position.