Flip sites and build a list. Create a squeeze page, and provide a link to that in your auction. " Like my sites, get notified of all new sites by clicking here" Or... Get insider deals on my most profitable sites by clicking here... And redirect them to your squeeze page. Now you have a list of website buyers. Offer a discount to your list to purchase your site before you list it. If no one bites, then list it on Flippa.
Flipping is good for small amounts or relatively fast money, but having a large list can make you money every day.
If you want a sustainable business then list building is the only choice. If you start list building now, in a few years you could have a business that basically gives you permission to print money. Website flipping is for short term financial gains.