We've had a pre-electronics Imperial Eastman Kwikrimp crimper for about 35 years. It has a hollow micrometer type dial that you set for the particular fitting, and when the plunger in the center comes flush with the top, you're at the proper diameter.
Don't know if they still do it or not, but, used to be all the major hose and fitting mfgrs published a list of the settings for the Kwikrimp corresponding to each of their fitting and hose combinations in addition to crimp diameters. It will crimp anything from small stuff up thru -32 (2") 4 wire hose, so I guess they were pretty popular for people who make a lot of hoses across a large range of sizes.
Between mobile cranes, boom trucks. backhoes, trenchers, dump trucks, and a couple semi trailers with hydraulics, we had 50-60 pieces of equipment with hoses. Tried to stock most any fitting that we might run into on any of the stuff, primarily because the local suppliers always seemed to have a sack full of adapters to sell you in order to get from whatever hose end they had to what you actually needed, all at heart attack prices.
The price of bulk hose and fittings is heavily dependent on volume. By buying an initial stock of $10K list, we were able to get 75-80% off of list, and the same discount for subsequent orders with a minimum purchase of $2K list. And, this was buying thru a distributor and not factory direct. Someone whose primary business is hose and fittings would do even better assuming much higher volumes. So, its not hard to see how an online seller can make good money on hose assemblies at half of list price. Given the fact that all the "Parker Stores" that seem to be popping up everywhere are selling everything at full list price, it wouldn't be surprising if they're operating on a 90% gross margin given the fact that they're all owned by large Parker distributors who are buying factory direct.