Stores and businesses are far more likely to test 50s and 100s to make sure they are genuine than 20s.

20s are a lot less suspicious...

its the most amount of money before you look suspicious and at most places when you hand them a 50 or 100bill they check it out first

The 20 is in wider circulation so used more often thus making it easier to find shops that don't check 20's.

I'd counterfit tens and fives. No one ever checks them.

I recently discovered that if you are the recipient of a counterfeit bill that you have to eat the loss, if you attempt to pass it on to recover your loss, then you are guilty of passing counterfeit notes. I tried to pay for my hotel stay while in Vegas with $100 and the clerk though that they were counterfeit, after 1/2 hour of checking and waiting the bills turned out to be ok. The Clerk would not give me back the suspected bills, would not let me pay by credit card and demanded that I give her more money to cover the suspected bills. After that fiasco was cleared up I went to my bank, my only bank, and told them what happened and asked them what they were going to do about them passing suspect bills, They said nothing. I asked the bank representative if they though it was ok for the merchant to claim the bill was bad and to ask for a replacement bill and they said that it was ok and normal business practice. I then asked what the banks position would be if I as a customer asked for $1000 in $100 and claimed that 3 of them were suspect and that I was going to turn them in the the Secret Service and that they, the bank, give me 3 more $100 bills to replace the "suspect" ones, there response was "You can't do that", I asked why not and then I countered with if the passing of counterfeit bills is illegal, who at the bank is going to jail for passing counterfeit bills? Just a blank stare... My statement to the bank rep was something to the effect that apparently the law against passing of counterfeit currency only applies to the public as a whole and not banks or merchants, again a blank stare...