HI Anthony
I’ve used this long established site which is managed by G3CWI for both buying and selling gear without problems:
G3CWI’s Amazing Online Flea Market
The amazing thing about the amazing online flea market is that there is no charge. There are the usual caveats which are covered on the website - beware of scammers, time wasters etc. I have never had any bother with them either as a buyer or seller.
73 Phil G4OBK