The majority of old machines need oil and some other sort of lubrication. The modern machines do not.
Not to defend the shop owner but she did tell you one truthful thing - many people over oil their machines and while sewing the oil flings everywhere inside the machine case.
I have a vintage sewing machine repair man and he even gave me a lesson on how to put just 1 drop of oil in the hole because he said the same thing as the shop keeper. The oil goes everywhere and that's how he knows people over oiled the machine.