$20 Serial Number Error

This is very common.

In my experience these are easy to find particularly in the new polymer series notes. In my experience I would say there is better than 1 in 500 chance to find it in a polymer note (particularly 20 for some reason) and perhaps a 1 in a 1000 chance to find it in the paper notes.

Having said that on e-bay they do sell at a premium. I guess from that perspective there are people willing to pay as opposed to look for it on their own. So it does not hurt to try to sell it. It may also be worthwhile to keep one as a collectible since it is listed as an error in the catalog.

A well know banknote dealer on e-bay has listed a sequential set of $5x5 journey notes for $90 ( for a face value of $25) or so calling it a misplaced serial number error. They also sold one set. And I put most of the sequence of 100 notes like that back in circulation just yesterday.

Lets put it another way. If I started listing on e-bay (I am not an e-bay seller) all the notes with misplaced serial number that I come across in a month the market will suddenly collapse