So, I recently got a Mandarin ratsnake. I purchased him on Saturday at a reptile expo and as of Wednesday he is showing what I believe to be advanced signs of a respiratory infection (clicking noises and gaping). Is it safe to assume he was sick when I bought him? How long does it take for symptoms to appear usually? I just feel so bad, I checked him over before purchase and nothing stood out as abnormal.

He has a vet appointment on Monday. If it is a respiratory infection, should I contact the seller? Should I expect anything from them or should I consider it a lost cause? This was a relatively pricey snake for me and I feel like he hasn't been in my care long enough for it to be anything I've done. But, I understand expos are stressful for the animals.

This is my first experience with a sick animal and it feels horrible. He's so small I did lots of research and felt fully prepared going into it but now I feel kind of overwhelmed. I would be grateful for any tips or opinions on the matter. I still consider myself rather new to the hobby and not very well versed in seller/buyer etiquette. If that makes sense.

Also, is there anything I can do in the meantime to help him out?