I believe I can accurately say - Virtually any brand and style of smoker will have some amount of like oily residue from manufacturing.
Most don't bother, but I would FIRST give the inside a quick rubdown with at LEAST a dry clean rag.
I , for MYSELF, would use stronger, but for someone else I'll say basic ammonia window cleaner such as old school Windex would do a final wipe best.
Then, BEFORE you put on any seasoning oil, let it run hot for a few hours, until you smell no more fumes.
Shut it off, let cool a bit w door open, for comfort and safety.
Then oil it and cook longer, like the guys say.
Apply it however you want, but prepare for a puddle inside when you heat it if you slather on overly heavy.
And keep in mind, the spray probably has a flammable propellant.
So I'd let it air out minute or two before turning back on.
This is what I believe is the best way.
It is NOT from years of Smoker experience like many here, but it is from a lifetime of many different metal projects, including BBQ's. Marc