There are absolutely no resale laws in Canada pertaining to mice. Like has been said, Mice have likely as well as squirrels and other vermin been in 50 percent of all Rv's in the world. The industry would have collapsed if mice had an impact on resale. Welcome to the forum but I don't get your post.
Also the "customer" has no disclosure responsibility in Canada. It is the dealers responsibility to know what he his buying. With 20 years in the auto industry, trust me when I say that salesmen have the rap of being dishonest but customers are the worst when it comes to disclosing issues with trades. But that is life.A dealer has ZERO legal standing when an issue is discovered with a trade in.