My supplier allows me delayed payment. I can NOT pay the supplier until I get paid. The only money I need to fork over is a deposit. I get a deposit from you. I go to my supplier, I say, this type of engine is required, this is what I need on it. They then track it down for me. I call you, or whoever wants the engine, and I tell you exactly what comes with it. I confirm that you want it. I then run compression and leakdown, I call you with the results and confirm that you want it. If you say you still want it, your deposit is at this point no longer refundable. Ofcourse if you run compression on it, and it is not what I said, then it’s refundable again, but it is in my best interest NOT to lie to you, so yea. At this point I have the engine cleaned and prepped, then load it into Allen’s van. Then we drive over to where you are and give you the engine and you give us $. Then we take your $, we take out the $50 or so that we profit and we drive over and pay our supplier.
We only make low ass profits b/c the supplier won’t yet trust us that we do volume. (trust me, it was hard enough convincing him to give us engines on delayed payment :D) Cuz we told him, we’re so and so, we’ll buy this many engines, so give us MAD discounts. And he said: I only see you buying one. And then we cried 
When we go for the next engine, he’ll drop his price down, and we’ll make more than gas money.