“If he had some way to run the registration, nine to one it was bogus.”
Is the bold part talking about the probability of being bogus? I cannot be sure. If it is so, what does “nine to one” mean? Thanks.
Yes, with 9 to 1 odds, if you bet $1, you will get $9 if you win.
Does the context make clear whether the speaker thought the event was likely or unlikely? I thought it meant that the registration was almost certainly bogus, in which case “nine to one” would mean “nine to one on”, or you stake $9 to win $1.
yes, Dozy I think you are right. I’m not much of a gambler 
Another related expression they use in the U.S. is “dollars to donuts”
“If he had some way to run the registration, dollars to donuts it was bogus.” Thus if I’m wrong, I’ll pay you off in dollars, but if I win, you only need to pay in donuts. Of course with inflation, soon 1 donut will equal $1.
A nice expression, I have to remember it,
I guess Homer Simpson would lay out $1 for a donut without having second thoughts though. 
Thank you all for your replies, now I understand that the speaker thinks that the registration is most likely bogus, even if it isn’t, the car has been stolen. Thanks again.