If you wish to check the legitimacy of a waste carriers licence in Wales, note the registration number of the licence and check it against the public register of licenced waste carriers on the Natural Resources Wales website. If the registration produces no matches, the licence is not genuine or valid. This should be reported to NRW.
Using this technique, you can also check the legitimacy of a waste carriers licence in England, in Scotland and in Northern Ireland by checking in with the relevant government body. As always, anybody that does not have a licence, or is operating fraudulently, should be reported.