There is no reason that they will not work as well as other pollution credits that have been around for decades. For example, I’ve seen power companies that operate nuclear power station sell their unused credits to other utilities and use the revenue to offset their operating costs. I have also seen them donate their unused credit to environmental organizations (and take the tax deduction); the environmental organizations then tear up the credits and get them off the market. In those types of cases, I think it works. The idea is that the limits will be reduced over time and these credits will become more valuable on the market.
I’m not sure that buying carbon credits from someone who premisses to plant a few trees is such a good idea.