eBay: Please enter a quantity of -1 or less

Here’s something you don’t see every day – I want to buy some boots and eBay are telling me to “Please enter a quantity of -1 or less”.

I’m at a loss to explain how this can possibly work. I can understand a retailer being out of stock, but how can they have minus one in stock, and even worse why are eBay suggesting I enter a quantity of minus one or less? Perhaps eBay want me to return an item instead of buying it?

Anyone with any ideas what’s causing this glitch or how to rectify it please do let me know. The retailer (my friend John) reckons he has none in stock, but somehow that’s been translated onto eBay as minus one.