That's different from fitting a recon part. A recon part as per geofs offering supplied by the plumber is no different to a new part supplied by the manufacturer as far as the law goes. It has to be fit for purpose and if it doesn't last a reasonable time the customer has legal redress against the trader.
A part supplied directly to the retail customer also has the same cover but its against the supplier. The plumber only has to fit it correctly. If the part fails in an unreasonable time then the customer has the capability to claim for the part and the fitting from the supplier. This can not be removed in contract, neither can the supplier claim he is trade only if the customer is clearly not a trades person.
repairs are a different matter if only because its difficult to show that the repair was the cause of the subsequent failure. reconditioned does not just mean repaired, it means its repaired, wearable parts replaced, tested, etc.