An online free-trial anti-abuse system design

Question

I am currently selling time based access passes to an online service at micro payment prices.

After payment the customer gets a set of credentials that is only valid for the purchased period. When the access pass expires the customer has to buy a new set of credentials. So basically the credentials are one-time(period) use only.

I would like to offer a free-trial of x minutes to this service so potential customers can realise it works fine, possibly increasing total sales.

My question is, how would you stop abusers?

That is, people should only be allowed to try for free once, and if that is not possible at least make them go through a process/test which (as in shareware) is too cumbersome or annoying for them to keep trying it.

Obviously there is always someone who will bypass it. I am looking for a solution for the majority of people who are either not IT savvy, time constrained, or simply too lazy to bother abusing it, instead of simply paying the tiny fee.

I have some approaches in mind but would like to be inspired by other people too.

The service is developed with LAMP.

Answer 1

I ended up using the smallest possible payment amount for a short time span, but enough to get the user satisfied at very low monetary risk.

In the time past since I asked I actually seriously considered using Flash cookies which very few people know (even that they exist) how to remove.

The other simple (although not-free) is using a SMS confirmation option which binds the user's mobile phone number. As a mobile phone number you just do not throw away like you do with email addresses then this is also a safe limitation method.

Answer 2

Put a cookie in their browser. Force a small delay before they can re-use your service, or make them go to the trouble of deleting the cookie. If they block cookies, politely ask them to allow them. You might have more business success if you allow several trials, with a minimum of hassle.

Answer 3

If you look around, everybody who gives out free trials binds them to a credit card - not to charge them, but to verify the user's identity. That's about the only feasible way to prevent abuse I can think of.

Any other idea will depend on the kind of service you are offering. StackExchange for example can offer a 45 day trial without a credit card no problem, simply because the effort to build a SE site is so huge, starting multiple trial periods (and having to configure a new site and build a new community every time) just wouldn't work.

Something similar could be unique login names that you can register during your trial period, and would have to give away if you don't convert it into a pay subscription, things like that. Really depends on the nature of your service.