I would also, never, buy a new cap
Between eBay, Facebook marketplace, and Craigslist you can get a used cap for under $1,000
Why spend $2500-$3000 New?
In the past with my Tacoma and my 1996 B2300 (AKA Ranger) I bought used toppers. But on my new F-150 I bought new.
Two reasons I can think of to buy new vs. used:
1. You need a shell NOW. Can't wait for one to pop up on FB or Craigslist (which may take a while, depending on the truck.) In the olden days, trucks all had either 6 1/2 or 8' beds and were pretty much the same width, so finding a "universal" topper wasn't too hard. But new trucks have a bewildering array of bed and cab lengths and widths these days, so finding one that fits may be a problem, especially if you have a less popular vehicle (like a Nissan Titan or Frontier.) You not only have to find a shell that fits your specific make, model and year range, but also your specific bed and sometimes even cab length (on some trucks, for example, the shell for the 6' bed on the regular cab is different from the shell for the 6' bed on the extended cab, because the back of the cab has a different contour.) If Winter is coming and you need something right away, waiting potentially months for a used one to "pop up" may not be an option.
2. You want to get exactly what you want: Side win-doors, for example, are a godsend. No more killing your knees crawling into the bed to get that one item that's always at the front of the bed when you need it. Ditto for things like roof rails, cargo boxes, etc. If you plan on keeping a truck for 5 years or more, the difference between a $2500 shell (that has everything you want) and a $900 shell (that is the wrong color and doesn't have the features you want) becomes negligible.