Thanks for the clarification :) You can allow various pricing packages for individual ads, free or paid, however these are differentiated only by price/duration (as you can see from the
ClassiPress admin demo). You can also set up membership plans which allow an unlimited amount of ads to be posted for a specific price, within the time frame specified
here. Categories which can be posted in can also be determined by membership status. There is no invoice functionality built into the theme.
The only way a customer would be forced to pay to edit an ad would be if they were upgrading from the original ad options, i.e. adding it as featured. Thanks.