Nothing comes for free. Soeone still has to foot the bills and anyone footing the bills for you to enjoy and make money would expect atleast base returns if not profits. So, most such free resellers if so, are based on fact that if you can generate enough revenue for them through advertising, you can have free reseller. Such hosts using free resellers can get washed away any time advertising revenues fall or parent co. feels otherwise.

Many offer private label reselling programme where they say it is a free reseller but then they put your domain and business to risk, because they act as your company and provide support to clients. Also, you keep profits but price slabs they give you is something which is difficult to get many clients.

Few may have it to fill up server but they rather control clients records, so any time they can knock you off and have control over clients, something that client may not realize since their sites don't get affected.

So, there is nothing like free lunch.