We buy big packages of equipment at a time (usually like 100 trailers or 30 trucks) and so we are able to get a great price. It’s not different than anything else you buy in large quantity. Since we bought them cheap, we can sell them cheap and still make some money.
We are a “wholesaler,” which means we sell mostly to other dealers. Those dealers then turn around and sell the same trailers (to people like you) at a higher “retail” price. We generally make $1,000-2,000 per trailer, compared to a dealer who marks up the equipment to make a $5,000-$10,000 profit margin. Buying direct from Rock is the best way to cut out the middle man and save a bunch of money, but there are pros and cons of buying wholesale equipment.