no its like a buying a car that has got a fault on it and then knocking money off for the repair, this happens very regularly. Its nothing to do with wanting to make the car better and knocking money of for coilovers. The fact is you have damaged goods for sale, If I was selling a damaged vehicle then it would be priced accordingly.
A decent set will sell for around 300 quid in reasonable condition, 400 with decent tyres.
The ones on ebay are up for that price, but it may not be the price they sell at as you have already found out by advertising on there. It like me putting my car up for sale on ebay at 25k, it doesn't mean it will sell at that and it doesn't mean that its worth that much.
You are forgetting that they aren't rare on here and aren't as valuable as you may think and a lip is damaged. Its maybe worth you repairing them and then putting them back up for sale on here.