App Store should allow for demo downloads

I am reluctant to buy some apps for the iPhone. If Apple were to allow trials for a few days that would be really useful.
It’s good that some developers are making “lite” versions of their software but proper time limited access would also be helpful.
I guess the lack of this now is helping developers make a little more money but can result in negative comments from people who have purchased and then sat they wasted their money. I’ve read a lot of these comments.
Hopefully this will come at somestage and until then I’ll wait to purchase some of the apps I’m interested in.