There are some people who end up buying all the best coffee bean grinders in search of perfection; there are people who can't resist a classic MIG welder. But those people were going to buy them anyway, and represent too few sales to justify any expenditure.

What you need are complementary goods. These people bought coffee bean grinders? Show them ads for travel mugs, for high-end coffee subscriptions, and fancy grinder-cleaning brushes.

Agreed; just to be clear, when I've had this happen to me it's showing an ad e.g. for the exact same model coffee grinder from the exact same store that I already bought one from. Clearly no intelligence involved there.