I'd be inclined to distrust polls, because since mobile phones (and the phishing accompanying them) there is no longer the pool of people to talk to that existed when it was possible to call a landline at random and ask a series of questions.
In the 1990s, say, a lot of polling was done by staff who stopped people on the street and asked them questions; later, this was transferred to randomised phone calls to landlines. But today, an awful lot of people don't answer phone calls from numbers rather than from the names linked to numbers in their phone's contacts list.
This isn't surprising; when I get calls from numbers it's usually someone wanting to tell me that my account with a bank I'm not with has been compromised, or that they're calling from the helpline for a computer operating system I don't use, or that my funds in the form of Bitcoin (ha!) has problems. These phriendly phishermen have removed me, and millions of others, from the pool of poll candidates.
On the other hand, the gambling companies are very well able to calculate the odds, because they're skilled in pouring money into their own pockets by fooling poor eejits who think they can beat the odds. So if they're giving better odds on one candidate than another, it's unlikely that the gambling magnates are wrong.