I used a "cash for mobile" website to send my old mobile for some cash but sent it freepost 1st class. Should have gone to the PO and sent it RD. Do you think they will claim it never got there? If they do thats £95 squid down the drain.
Just to add. These company's are legit. If people send in their mobiles and they claim they never arrived there will be complaints and they will be looked at.