If you are looking to setup your own Elite Proxy then you may want to give some thought to getting IPs from C class IP ranges. It isn't a topic that is discussed often, but not having IPs on your server from different C class ranges could be leaving a very big footprint on websites.
IPs are divided into different ranges, A B C and D. By using ranges we are able to log network IDs and network activity. Every computer online has an IP which allows it to communicate with other computers online, essentially functioning as an online mailing address or phone number. Most people know that by going offline and then back online you are able to change your IP, but usually the new IP you are assigned is within the same range. This allows companies and other people to more easily identify your activities as even after changing your IP, it has not changed significantly so they are unable to find any similarities or patterns in user activities. It is more than possible that this is exactly what websites uses as part of their system to filter out spam. Making sure your proxy server has IPs from different C class IP ranges helps to prevent this problem.
As already stated above, not changing your IP significantly may mean websites is able to make a connection between two or more accounts you use to post on websites with even after you change your IP (since your new IP isn't varied enough from the old one to make you look like a completely different user). This also applies to proxy servers and is why you should consider getting IPs from as many different C class IP ranges as possible. Usually, IPs that are assigned to proxy servers are normally within the same C class range, which is what you do not want. Remaining anonymous is very important for anyone posting ads in quantity on websites, so be sure to get a Elite Proxy with IPs in different C class IP ranges.