Buyer is sabotaging my store

[tikitommys]

There is a buyer who keeps committing to buy items while there is one unpaid item case against them closed and another open in my store. I obviously need to block this buyer. There is yet another item pending payment from the same buyer.  Should I cancel that sale before or after I block this saboteur?

 In all my time on eBay I’ve only had one upset customer because I was unable to locate the shirt they ordered so I canceled the sale with apologies but that buyer relentlessly harassed me afterward and I had to block them. I believe it is the same person sabotaging me now using a new name. 

[shoppingbomc2014]

Block them.  Don't cancel the sale - it will count against you.  File unpaid item claim and let it time out.  That way, they get the "ding" against them.  Since they have already tried to buy from you, they can continue to contact you for a bit, but the block will prevent them from purchasing from you.