bug free product...
do you mean "free bugged product"?I think the important thing with any engine (if you are the seller) is that you are using it yourself for a proper game, because then you need it to work properly and thus are updating it and fixing bugs etc. If you are not using the engine for a game, then your incentive to fix it is less. However, if you have customers then you have made a commitment and should honour it imho.