Factual error: The Sanderson House had been turned into a museum complete with a gift counter. The museum had been closed for years (note the dust and spider webs). The fluid in the lighter Max gets would have evaporated after a few months as Zippos are not airtight like a plastic disposable lighter would be.
Factual error: When the witches follow Mary into the alley after singing I Put A Spell On You, Mary Sanderson said she smelled Scrod, a bottom feeder that would be good with margarine. 300 years prior to that, butter would be the topping of choice as margarine hadn't been invented until the 1800s, when the sisters were dead.