Bad experience with buyers

I work on PPH more than 2 years, and I've never complained about that kind of things before, but for the past few month on this site I had too much bad experience with buyers.

Sometimes clients reply very late or never reply you back when you're in the middle of working process, sometimes they delay your payment (thankfully it happened to me just once), but now I constantly come across rude clients, who talk to you very impolitely and rudely in the work stream, making your working process a total nightmare. I know that they too could have a bad experience working with freelancers on here, and when you start working with a new person it's always a risk because you don't know them, but being polite and keep your conversations professional is very important for productive work. 

I wonder if any of you faced the same problem?