From HMRC website --
"If you buy a vehicle to sell on, you can reclaim the VAT on your next VAT Return. You must be a VAT-registered motor dealer."
you still have not understood the difference between a purchase of a used vehicle from a private individual and a trade seller in terms of the SALES TAX known as VAT. Only VAT registered companies can charge and reclaim this tax.
e.g. dealer A gives you 5k part ex and then sells it to dealer B for £5k plus VAT just to get rid of it, i.e. £6k. Dealer B, if VAT registered can reclaim the VAT back. Dealer B has effectively bought the bike for £5k net of tax. Dealer B then adds £1200 to the bike and sells it for £6200. Dealer B will need to give one sixth of the profit to the VAT man i.e. £200
If you sold the bike to We Buy any Bike, as a private owner for £6k then they are not able to reclaim any VAT. You are not VAT registered and all of that £6k is your's to keep without handing any tax over to HMRC. WBAB's net purchase price is £6k so they would have to sell the bike for £7200 to make the same profit as Dealer B.
VAT "remaining in the bike" is a fictional concept. Value in the bike is the asset value which can go up or down in relation to supply and demand. So, yes, a new bike does not automatically decrease by one sixth when you ride away. Less common nowadays but it was certainly something seen in the mad days when demand for bikes like the Ducati 916 were in short supply.
