You don't need money to change hands for a transaction to be taxable. The sort of barter-based system you describe would also (in theory) be taxed. The only dif

You don't need money to change hands for a transaction to be taxable. The sort of barter-based system you describe would also (in theory) be taxed. The only difference is that tax enforcement would be much more difficult under your system. That would work well for a while, but if your service got really big, and became a target for enforcement, you (or your users) might have serious tax problems.