"Cool"? Well...
1 - Lionel GM&O Legacy GP35 from an acquaintance. Good price; have the correct AAR(Alco) truck side frames to replace the Blombergs on order from Lionel Parts. Cool.
2 - Finally found an Atlas NYC "cat's whisker" F2 NIB A-unit; from individual. Faulty gears (chewed up; from factory, I guess) on one truck; will not move more than 1". Not Cool. Seller left me out in the cold. Not Cool, again. There's a word or two for those guys, but I'd get kicked off here if I used them.
3 - Not a purchase - but discovered that my Lionel ATSF Alco S2 switcher has crumbled internally at both gearboxes, or so it seems. Dead, jammed, mechanically (electronically very durable). Not Cool.
4 - Won a brass tender at auction, only to find out that it was mis-listed and described as "O scale", when, in fact it is HO scale. One forgets how small HO is (I don't handle it much). The seller said mail it back for a refund. So, not Cool, but it could be worse, if resolved acceptably.
You had to ask.