Unfortunately the only way to tell for sure, is by redeeming it! Sometimes there are characters shown on the slip, which can be a clue. Also, do think this is from a DVD or a Blu-Ray?
It will help you in the future if you make a note of what movie it was and if it was dvd/bluray because of the point values and you can only redeem once per movie per platform. If you have one that isn't common your bids will skyrocket. Like tpattnaik said, some of us will still bid randomly, just not as high because we don't want to burn a code and not get anything.