Depends on the age of the vehicle. A 2-3 year old vehicle, I'd expect a single owner. A 10 year old vehicle, I'd expect more than one.
Our '03 Silverado had 2 prior owners, original owner had it 3 years, second owner had it 7 years. Good service records. Overall condition was great, so being the third owner wasn't a concern.
A 15 year old vehicle? Don't care about much except if the vehicle was a rental/some other type commercial vehicle and the title's clear.
I'd also consider where the vehicle's being sold. Some states, like Mass., require the dealer to actually title the vehicle in its name, meaning the dealer becomes a counted owner, despite the fact I wouldn't count the dealer as much of an owner. But Carfax does, so the owner count may be artificially high in that type of state.