Honestly, even if eBay did still take commission, it would be worth it for the stress this is causing you.
I used to sell Buffy the Vampire slayer memorabilia, I went to conventions to meet the cast and would get in person autographs to sell, which helped to cover the cost of my personal collection. I did all of this on eBay.
You seem very concerned that the first person might run off without paying. Obviously you don't hand it over until they have the money out if you decide to sell to them. Do you have a ring doorbell or similar that would record everything? If they want to inspect it first, you could always arrange to meet in a public place where you can go indoors making it harder for them to do a runner. I would also check their Facebook profile to see if it looks fake. If they have it locked down, ask them to add you as a friend and if they ask why, explain you've had issues with scammers in the past so you like to check that buyers are genuine/real people - say they can remove you after the sale. If they don't want to or delay doing it, I would ask myself why and consider trusting my gut. Google their name with scam or Facebook scam after it to see if anyone has posted before to say they are a scammer.
As for the second person, if offering you £50 less AND they want it up front, I wouldn't even consider that. EBay it - as far as I know private sellers no longer pay fees, but even if you do have to, it won't be £50 and you won't have to send the item up front before payment.
If you do post it to a buyer, insist it is sent by a service with insurance (eg Special Delivery in the UK) and don't accept offers to pay less postage to get it sent in a cheaper way. If it went missing (or they claimed it did) the standard insurance on 1st class or even recorded delivery is bugger all, and certain items aren't covered anyway. If sending abroad, check very carefully the options as some don't offer tracking once outside of the UK, don't need a signature, etc. Put the cost of the postage on your listing. Always get and keep your proof of postage!
Well that ended up longer than I intended - whoops! I hope you sell it successfully and have no problems getting your money.