Here's a possible system: - Free accounts exist. They have mostly full privileges. - A given user can only receive so many requests per period of time

Here's a possible system: - Free accounts exist. They have mostly full privileges. - A given user can only receive so many requests per period of time. A given user can only receive one request per user for a given period. Others are informed that they will be put on a waiting list. The site could play games with the waiting list, like purging inactive accounts or increasing the priority of requests similar to ones the user has already responded to. - Paid accounts exist. There is at least one incentive to pay: you may skip a waiting list every so often. The cost should be enough to reduce the incentive for account cloning and keep the spammers out, as it exists only for that purpose. Desirable demographics (really a euphemism for 'women') would pretty much not need to pay. On the other hand, the site is especially attractive to them because they are not bombarded with messages. Less-desirable demographics would still be able to use the site without paying, but they would be able to pay to not wait around as much.