Here is how I think it should work...
In your "Edit Catagories", you should place a cost of an ad, say $10.00.
Then you go to your "Edit Usergroups" and you place a number in the "Max Ads Limit?" box, that is the maximum number of free ads that a user in that group can have at any givin time. Any user can still purchase additional ads as they see fit, beyond the "Max Ads Limit?" placed in the box by their user group.
The "Max Ads Limit?" should only apply to "Free Ads".
I am sure no-one wishes to limit paying customers.
I have done some experimenting with the limit.
I just did a test usergroup. I set it's limit to one. I posted a test ad for three days. After that I went to attempt to post another ad. I got the "you have exceeded your maximum alllowed limit of 1 ads."
It didn't even give an option to pay for an ad. Why would anyone put a limit on the number of ads that can ever be posted. I don't understand how the photopost developers could figure that was what was wanted.
If they really think that is what the majority wanted, there are enough people out here that want it limited as I described above. Perhaps they can give us a choice as how to limit the ads.
I am giving a lot of thought as to how advanceing through usergroups could be used with this to work well. I am not sure it can be done without having the ad limit defaulting to a pay option.