You are correct. one sale isn't enough. That is why Mods leave these kinds of suggestions open for a month+, to wait on more sales.

Unless you plan on selling it soon, or Gon Freecss sells his soon, this suggestion will stay up.

Offers won't matter, and an outdated price doesn't reflect the current market of said hat.

If you feel this price is inaccurate, I suggest you sell your hat, then make a counter suggestion within the next month or two. If you can't sell it within that time, you are free to make your suggestion whenever you do sell the hat.