eBay
automatically includes Click & Collect on an item's listing unless
(a) the item isn't suitable for the service ; or
(b) the seller has gone into the Site Preferences section of their account to opt out of the service.
I suspect that many sellers aren't aware of that though, meaning that they'll be surprised when a buyer wants to make use of the service.
https://www.ebay.co.uk/help/selling/posting-items/setting-postage-options/click-collect?id=4180
I also suspect that many sellers are unaware that it won't cost them anything extra
to offer the service. Neither will it involve them in any extra work, as eBay automatically puts the store address (instead of the buyer's one) on the address label that they'll print out.
https://www.ebay.co.uk/sellercentre/postage/click-and-collect