Always buy direct from DVLA if possible. Years ago I had a plate which was bought from Regtransfers. Assignment fees were paid and I had it on retention, which DVLA had a fee of £25 per year at the time. On renewal, RT insisted you send the certificate back with a £75 payment to renew the retention as the plate was still in their name and you was only a named nominee. The £50 was their admin fee to sign and post it. After plenty of arguments, I had it placed on a family member's car and eventually took it off. Certificate was in my name with no extortionate fees.