Thanks for all the interesting points. Yes I was hoping to find someone on here who's selling. Some of the way the eBay listings are written doesn't exactly fill you with confidence! You're right about the detail, explanation and photos of all issues - they add so much credibility to a listing.
Regarding the eBay price you pay when you win a bid - I think it comes down to what the previous winning bidder has set as his/her highest bid to. For example lets say Joe has added a maximum bid of £100 to an item. The listing had a starting big of £50 so eBay will only bid £51.00 on Joe's behalf, i.e enough to be the highest bidder. Then, if Jane comes along as says, "hum I want this, I'm going to put £200 maximum bid on it", eBay will then set her bid to £101.00 - enough to beat Joe's bid, but no more. If someone else, John, comes along and thinks "I want to enter the running, I'm going to bid £150" - eBay will then actually just change Jane's bid to £151.00, but she'll still be the highest bidder. John's bid doesn't even get him anywhere. He'll need to bid again with a higher bid than Jane's £200 to actually be the highest bidder. So I think the explains why some people are seeing big leaps after bidding on lower current bids.