Unfortunately, I think Sid has a respiratory infection or something going on. He was making a hissing/wheezing sound while I was holding him. I guess a trip to the vet is in order. Can't expect too much from people on Craigslist, I suppose.
Nancy is a nice-looking "Circle-Back"; I've got a big girl very similar to her. Sid might not have a RI; some large boids just make a sort of hissing or wheezing sound when you hold them due to their own weight. My JCP and some of my bigger Boas do this when held, and so does my big female Northern Pine AND my Eastern King, and all of them are perfectly healthy snakes. It's just a big snake thing. Monitor him in his cage and see if you notice any coughing, sneezing or wheezing when he is NOT being held, or if you can see any exudate from his nostrils, and that will give you a better idea if he has any infection or not.
And Lorgakor, there's no reason for the snakes to have mites. It's no more normal for snakes to have mites than for us to have fleas, so if the snakes were taken care of, they should be mite-free. Reptile mites do not bite humans, anyway, and are very host-specific. I put my snakes on the bed all the time. With Boas, you can actually tell when they have to "go" fairly easily, and just don't handle them or put them on the bed or carpet when they look like they're gonna drop a load. I've spent many a Sunday afternoon kicked back on the bed, propped up on pillow watching the NASCAR race on tv, with either a young Boa or a Water Snake AND the cat!
Toni, Wow, they're pretty!! +1 on the noise. I had a large brooks king I caught of 84 that I kept for awhile some years ago in Florida. He was a monster at just shy of 6', healthy, but also made a wheezing sound when breathing. Another friend in Ft Lauderdale had a boa that did the same thing. Cheers,
Thanks for that info, PBL and Terry! He doesn't make any noise at all in his enclosure so I had actually decided to hold off on the vet for a few days and keep a close eye on him. Thanks for letting me know that this can be normal.