I’m a working as a freelancer in odesk.com and elance.com. It is a great experience to work with a good client. I want to give you some tips here that help freelancer to find a good client in a freelance marketplace.
If any freelancer follows the tips that I described below it help them a lot to find a good client. I hope keeping these things in your mind will give you better experience.
1. Verified Payment Method:
The first and one of the most important things is to check if the client has a verified payment method. This will ensure his payments in hourly contracts, and increase surety in fixed price contracts.
If the client is new and doesn’t have a verified payment method, you may ask politely about what he is thinking to get his payment method verified. I have found some clients who are actually under process of getting his payment method verified.
2. The Country he lives in:
I found this a vital point for choosing a client. Choosing a client from a HIGHER ECONOMY country may be good for a lot of contractors. 
3. Rating/ Feedback he received: 
It’s always better to work with someone who already has experience working with other contractors and has received good (4 and above) feedback and ratings. This makes things easier.
4. Rating/ Feedback he gave:
I know most people don’t consider this. But for me, this is one of the most important things to consider when I choose a client.
You’ll find a lot of clients who often provides bad rating/ feedback to the contractors and often criticizes them. When you read both comments of client and contractor, you’ll see that the work was completed successfully without any problem and there was everything alright. But then also, client gave low rating just because he doesn’t want to praise his team member. I think this is a BOSS type attitude, rather than a TEAM LEADER attitude. And I ignore these types of clients mostly. They will often try to keep you in mental pressure and take advantage of your work without proper valuation.
5. Fees he pays to contractors:
This is another vital point I consider. When you try to apply for a new job, and see client’s previous records, you’ll see how much he pays to contractors. Some clients are there who pays $30 for a $300 job. I try to avoid them.
Finally, there is always exception. There are clients who are good but had some bad experiences with some bad contractors. You’ll understand that from their comments in feedback. I think they will respect you more than the new comers, since they know the pain of the bad contractors. So, if you are a good contractor, they’ll do everything to ensure you are happy with them.