Our software does not have on-site Paypal purchasing ability for classifieds listings by design, since that ability is already available using another more appropriate listing type. We are not alone in how we define what a classified ad is in our software, our definition is almost identical to EBay's listing definitions:

http://pages.ebay.com/help/buy/formats.html

In our software, classified ads function a lot like Print classifieds. They are meant to put potential buyers in contact with potential sellers. The seller can choose who to sell to, instead of being obligated to sell it to the first person that gives an offer. By design, Classified ads are not meant to be "automated". Any transactions would be completed outside the software installation, after both parties have agreed on the price.

If you want a more automated process that allows a buyer to purchase something right away, that is specifically what buy now only auctions are designed for. Using buy now only auction will provide more protection to the buyer and seller than the open classified ad format. We suggest using the auction format but use a buy now only auction. The auction listing will have the buy now (or buy me or buy this or get this…or however you want to label it) button and will not have a make bid button. The first person willing to purchase at that one price will click the button and close the auction.

1. The buyer and seller are protected by the feedback system provided by the site. The classified format affords neither the seller or the buyer to rate the other after the purchase is over. Thus each classified purchase is a shot in the dark unless you personally have dealt with each other in the past.
2. You as the site can charge a final fee on the purchased item if it is a buy now only auction. You still have the option to charge up front by duration or flat rate as you can through the classified format.
3. There is no competitive bidding for the product sold. The first one willing to pay the price clicks the button to purchase it.

You have complete control of the text used within the system. This allows you to label the auctions buy now only feature as anything you wish. Just change the text where ever it appears to what you are naming your feature. Unless you want to allow classifieds also you only need any of the auction editions of the software to accomplish. After labeling changes if you want to make them there isn't much else to do.

Although it goes against how we define what a classified ad is, there are 3rd party created addons which do allow a classified ad to be purchased using Paypal, similar to how a Buy Now Only auction already works. Browse the GeoAddons.com site for that and other 3rd party addon functionality. Note that we do not support 3rd party addons, if you need support please contact the 3rd party that created the addon.