Selling on line

The advantages of ebay is that purchasers buy through PayPal and they advise you not to accept cash or (especially) cheques.

Generally I post anything I sell. I only say collection only if it something heavy where post is impractical or extremely expensive.

You do not say what sort of things you want to sell. Auction sales are good for furniture and things like that. There is bound to be one local to you.

Alternatives if you just want to get rid of stuff whether you sell or not are Freegle and Charity Shops.

Look at eBay. They will answer your queries. Others use Gumtree or marketplace. I use eBay and have had no real problems with it.