If you feel bad about polluting the world with your car you can buy carbon offsets, which reduce carbon dioxide emissions by investing in technology or by planting trees.
Some people believe that there are many companies out there that take your money but don't actually do anything.
This is why I believe that there needs to be some accountability. What would be a great idea is a firm that carbon offsets by planting trees but, to allow customers to verify that everything is legit, the customers can walk into the plantation themselves to look at their own trees. Each tree will have on its trunk a label with the customer's name written on it.
I have been searching on the Internet and there does seem to be some sites that allow you to do this. E.g. at Rainforest Rescue.
Giving customers an opportunity to inspect for themselves in person I believe will wipe away any doubts about legitimacy.