Ebay no longer allow cash on collection.
You have to pay through Ebay checkout.
If you do ignore the rules and pay the seller cash, you have no buyer protection and you are both carrying out an 'off Ebay' deal.
Personally, I would contact the seller and tell them that I would rather abide by Ebay rules and pay through Ebay.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)