Be as honest as you need to be
Don't claim it's immaculate if it's not. An obvious lie will make buyers question everything else you've said about the bike.
Scrupulously list any flaw or wear that buyers are likely to notice. Anything else is caveat emptor.
An eBay auction is asking to have your time and money wasted by fantasists. If you must go eBay, use a classified ad. If you go via Gumtree, expect to be offered job lots of hatstands or Staffie puppies in exchange, although there are plenty of real, honest punters there too. If you have to re-post your adverts, do not go off on one about "re-posted due to time wasters". That's of no interest to genuine buyers and makes you sound like a mental.
Don't be put off by foreign gentlemen offering you a sack of cash to put your bike in the back of their lorry. It's common enough now, and their money is as good as anyone else's.
Negotiating tips: don't agree to accept a figure unless they're actually offering to put it in your hand - ask if they are. Make that mistake and they might "go away to think about it", then come back later (or send a mate) and start haggling down again from there.
Sell to the first person who actually puts money in your hand. Don't "hold" a bike for someone who might be on the way to see another half dozen.
Test pilots need to have 3rd party insurance to ride the bike. You're (also) committing an offence by letting them ride if they're not. It's an absolute offence, there's no defence of "reasonable belief", and having them sign a statement is likely to affect the sentence, not the conviction. Get (genuine) details from them so that if a NIP and s172 comes through the door two weeks later, you know who to point at.
When the deal is done, hand over the new keeper slip and always complete and send off the V5C yourself, never trust the buyer to do it. Its your responsibility, not theirs, the DVLA will come after you. Get (and keep safe!) a free "certificate of posting" from the post office, in case Royal Fail or the Department of Various Lost Articles do what they do best.