Agreed. Also on the personal level, while it could save you some money, you're not only offsetting mass transit funds to the taxpayers (or other passengers), b

Agreed. Also on the personal level, while it could save you some money, you're not only offsetting mass transit funds to the taxpayers (or other passengers), but also taking a risk that the card you are trading for is from where they say it was from and that it contains the amount of money the other person claimed. You're also potentially (haven't thought through all of the details yet) losing out on the convenience to tie your Clipper card with your credit card, take advantage of BART high value cards ($64 value for $60), and being able to take advantage of paying for transit in pre-tax dollars. And unless this could be made very simple, you're going through a lot of daily stress just to save a very small amount of money which can distract you from doing things that give you more value.