Not all proxies created equal

When trying to register/post on a few sites that have previously blocked my IP I noticed that none of the anonymous elite proxies work. I'll try to register using the samair.ru list, for example, and the confirm email never comes. Or the post gets bounced.

But when i use a service like cantbustme.com or hidemyass.com i have no problems.

So do the proxy browsers have unique characteristics that bypass the aforementioned filters?

Why would a port proxy fail but these work? socks maybe?

free proxy = free stuff = not good
you should buy a service , because free proxy can be blacklist ip address ,many people used it