In fact I had suggested long ago that Nokia (then OVI) Store should have a policy in place with the Developers that for each and every paid application, there should be a FULL FUNCTION TRIAL VERSION. In both the cases that you have mentioned ( wether it works OK or user doesn't like it) there is no need to go into the hassle of any RETURN..
Refer this thread ..
BTW I never got any refund for a Non-working application mentioned there-in..