This is only a suggestion but if implemented could make the script a World Leader.
Make it user friendly.
User configurable image limits.
Ability to change text limits in admin panel thus avoiding messing with code.
Payment manager: decide what payment gateways to be allowed, and prices etc.
Charge for ads by percentage of item value.
Page view statistics, divided into member/guest visits, browsers etc.
There is probably more, perhaps others could add their suggestions below?