Not really. I saw him sell for 45 million recently. It's all a matter of the time the auction ends, or up to the seller him/herself.
Different websites have different prices for villagers, so prices here may differ from Tumblr, GameFaqs etc.
Yes. Alot of people want Marshal, and alot of players join the community every single day, so demand for him will always be high(unless everyone in the community actually has him.) So yeah. It depends on the seller, the time you were online, the auction's duration etc.