Selling a business starts long before you put your business up for sale. I've encountered hundreds of sellers in just the last couple of years and what strikes me is that most of them are not ready to sell.
To get the best value out of your business you need to plan well ahead, collect you stats, keep detailed records, keep copies of contracts, have operating manuals for all the moving parts....
Sellers of websites in places like Flippa very, very, very rarely have all of that.
And because they aren't properly prepared they lose out on the best deals. Buyers will pay more for a business that's properly organised and that is not reliant on the seller's goodwill for post sale "support".
James Caan of Dragon's Den fame is starting a business called Bluebox to help companies prepare for sale. Guess when they start preparing the business? Three years in advance! The larger the company the longer it takes, but even for the $10K or $20K site, spending a bit of time preparing will be time well spent.