Why are users invited to 'purchase ads' in classifieds?

Hi

I'm not keen on the way my users are invited to 'purchase' their ads on my site. I think this is very off-putting to people wanting to list a free ad.

Is there a way of changing this?

Also, is it still true that there is no way to have both free and paid ads on one installation? Is this likely to change any time soon?

Thanks

Sally