Review of Best Seller TV Program

I bought the elevate 5cm for 20 $ and I found the second day that others (sell online )are selling it for 12$ ...and the same quality..that means there's an 8$ difference which is not called best seller..it's not right... 8$ worth ******** L.L. and I also discovered other goods are more expensive in best sellers ..so it's not the best at all