I recently start working in freelance , and I think that the payment doesn't worth it ,and the employers are not generally serious, you keep waiting for the pay

I recently start working in freelance , and I think that the payment doesn't worth it ,and the employers are not generally serious, you keep waiting for the payment , and they usually don't pay , now I deliver work like a demo , it only works for a few days , just so that I can be sure they pay . ps: what websites do you use ?