I think you're being too optimistic. Second hand parts are (rule of thumb) worth half what new ones are, a little bit more if they're rare and a little bit less if they're not. And if they've got a lot of miles or wear, a lot less.
At £500 for the pair the buyer may as well stretch to the new ones- it's not a huge jump, and you then benefit from them being new, having the warranty and so on.
I think you're being too optimistic. Second hand parts are (rule of thumb) worth half what new ones are, a little bit more if they're rare and a little bit less if they're not. And if they've got a lot of miles or wear, a lot less.
At £500 for the pair the buyer may as well stretch to the new ones- it's not a huge jump, and you then benefit from them being new, having the warranty and so on.