The sales person removed the film and use a cloth with alcohol to wipe it before putting the screen protector on. I questioned him but he said that's the way to remove dust (??).
Alcohol would be useful for removing greasy fingerprints (which shouldn't be a problem with a 3GS), but a cloth or facial tissue slightly damp with plain water is enough for removing dust.
I was concerned and later on found out on internet and in the iPhone booklet that we should not use alcohol to clean iPhone.
It won't damage plain glass, such as on the previous iPhones, but I wouldn't use it on coated glass without knowing something about the coating.
Is alcohol abrasive please?
It's not abrasive, but could soften or dissolve some coatings.
And how bad is it to the oleophobic coating please?
Even if it did no damage, I wouldn't use it again.