Review simple paypal checkout flow [on hold]

I have a website where users can place classified ads similar to craigslist. Now I try different ways to monetize the usage. I have added paypal payments for two functions: (1) Pay to include a video with your advertisement that can be in mp4 or ogv format (2) Pay to display your advertisement among "trending ads" on the frontpage.

I recently deployed a mechanism trying to make users pay for the above new functionality. The flow is according to the following:

  1. User clicks "advertise here"
  2. User fills out form for placing an ad
  3. User agrees to terms and clicks "Display my ad among trending ads"
  4. User is directed to a preview page where he can preview his advertisement and press the paypal checkout button and pay. When it is paid a confirmation js alert is displayed and the paypal checkout button disappears and the "place ad" button appears.

Or, if user uploads a video instead of images, the preview page will also include the paypal checkout button.

Is the above strategy the best I can do or should I charge for some other function or do it any other way?