To be honest, you are in the driver's seat. There are a lot of collectors with deep pockets. If you don't like the game and want to cash out, it's simple; take offers, then with the best offer add a bump and you'll get what you want.
There comes a place and time when the price will level, or only go up incrementally. Sell at the Apex. With the funds, you can get 2-3 super awesome collectibles for the price of 1.