There is a difference between offers. If the trial is clearly stated and you are using an "ethical bribe" like giving away loads of freebies to make people try the product, it is OK I think. But it has to be super-clear that the customer will get billed.
Lee McIntyre UK marketer used to do a hot $1 trial offer, and he moved into a direct selling method, because there were loads of people complaining, even though the trial was clearly stated.
If you want to maximize your profits from membership sites, the best option is to get a drip content software. That way people will look forward to the next module, instead of having to consume the content at once.
Another important thing about trials is that the majority of people don't even review the content during the trial, so you need to create a system to make them log in and get excited.
Hope this helps.