I went back to the store and did some more sleuthing. The screws are definitely machine made. I'm having a hard time telling how the wood is cut but at this point I'm thinking this is a modern piece. Based on some other conversations I've had, I'm coming to the conclusion that this is probably a 20th century (1920s-30s) reproduction of an antique piece. There doesn't seem to be enough variation in the construction to warrant calling this a 'handmade' piece. The insets where the inlay is missing is remarkably regular all across the piece and the dovetails seem pretty symmetrical to me. I've included some pictures in case there is something to give someone an 'aha' moment, but 1930s is the conclusion I'm coming to. If that is the case, I'm not going to buy it. While $600 is a steal for a real 18th-early 19th century desk, I'm not so sure it is for a 20th century reproduction, even if it is solid mahogany. If it was real I could call it an investment or a family heirloom, but if it isn't, it's just a desk-one that is smaller and less functional (it's short and my legs barely fit under it) than the one I currently have. It's also one that is missing a lot of inlay and needs to be refinished, which equals time and money I'm willing to spend on the real deal but not this.
I'd like to thank all of you for your great advice! This has been a great experience, I've learned a lot, and I'm excited to be here. Thank you also for helping me avoid making a large financial mistake.
Dovetail on drawer
Underside of desk.
Underside of small drawer.
Top of drawer and missing inlay.