Go to the links below to set up buyer requirements etc.

https://www.ebay.com.au/help/selling/resolving-buyer-issues/blocking-buyer-ebay?id=4082

https://www.ebay.com.au/help/selling/listings/creating-managing-listings/setting-buyer-requirements?...

https://www.ebay.com.au/help/selling/getting-paid/resolving-unpaid-items-buyers?id=4137

I see you are selling pick-up items, it is best for buyers to pay cash on pick-up after they have inspected the item - if it is not suitable or not as described then they are free to walk away from the deal.