Unfortunately, listing fees for vehicles / motorbikes are non refundable, and payable sale or no sale. Same if you listed your item in your local paper, and it didn't sell, the paper would not refund your advertising fee.
Fully understand the annoyance here, the buyer was obviously wishing to see what the lowest amount you were happy to receive, should have been blocked sooner from returning to your sale, but hopefully as you've listed your lovely bike again, you've blocked him now ? If not do so here, asap:
https://www.ebay.co.uk/bmgt/BuyerBlock?
@daharr-3578