The way I look at it is that what I sell is bikes, but what I buy is parts either separately or in rideable form. Even when I repair other people's bikes I keep all the old parts and enter whatever components are recoverable from them in to my parts bank, and withdraw other parts from my parts bank to use on their bikes.
Whatever 'bikes' I own are merely collections of temporary withdrawals from my parts bank, until I assemble a bike for sale.
My last build off bike, Ten Turing, has aluminium wheels from my neighbour's bike simply because his rear wheel bearings were toast and we could not remove the freewheel. I had a pair of steel wheels in stock that I had not yet stripped down, so we exchanged, and he was up and riding the next day. Two weeks and much effort later and I had that freewheel off.