I can't speak to Mike's or how Specialized does it (with shops that buy their bikes) but the shop I worked at was net 30 for any "over the counter order." I don't recall if Project One bikes (it was a Trek shop, but not a Trek owned shop).
Over the counter - A SKU'd bike from one of the manufacturers we carried.
I know the owners told me that they would commit to X number of units via their pre-season shopping, that typically occurred in May-June for the upcoming model year. The model year was typically August 1st - July 31st. I also recall them saying that if they bought X number of a certain "tier" of bike they got a better pricing and also to maintain their tier of pricing they were required to buy X number of certain models, often sight unseen (colorways not known). We also had to have so many "halo bikes" on the floor. At the time I worked there it was the SLR 10 which had just come out, ironically of the three we brought in on the first wave they all sold very quickly.
So to answer the question, the money stayed in the shop. Also, we were a 100% paid in full on any bike or color we didn't actively stock. As well as "low volume sizes" (typically anything that wasn't a 54 or 56cm in men's or a 47-52cm in ladies). Trek had a few stinker colorways over the years I worked there that we didn't want to sit on if the buyer got remorse.