Probably not widely. They likely have some sort of source of information that they use like for example: 'the current published price on bloomberg by Intercont

Probably not widely. They likely have some sort of source of information that they use like for example: 'the current published price on bloomberg by Intercontinental Exchange'. Though this may not be the exact market price of the REC at that particular instant, it would be within a couple cents or so. Also with such a small market the amount you could get per REC changes significantly based on volume. Anyways, you as a customer with a utility bill probably have 0 say in what you sell your RECs for. You already would have signed away those rights when you signed the lease on your solar panels. (at least that's how it all works to the best of my knowledge)