I bought a new mower (Poulan Pro 18.5HP 42"), but it was last year's
model. It is hard to start usually. If it doesn't start on the first
try, it takes another 10-15 tries to start usually. And almost every
time I shut it off, it backfires. I read a post about the backfire, so
I'm thinking to throttle it all the way down and let it die that way
instead of shutting off the key, to see if that helps. Usually I turn
it off at half throttle, but it still backfires.

As for the starting issue, I wouldn't be surprised if it's being
flooded, but why is it being flooded? Where should I start?

BTW, the store that I bought it from was closing, so I can't take it
back for them to check out. I can probably get it to a service center,
but if there is something simple I can do, I would much rather do that
then trying to get it to the service center.