If you go for a used bike, get one that was decent quality when new. There is no point buying a low grade used bike.
Get the right size with no obvious crash damage and no excessive transmission wear.
For a utility bike, ensure that the bike can take medium size tyres , fenders and a rear luggage rack. There is no point getting a nice competition racer for hauling groceries.
Major brands are usually good but there are lots of decent minor brands.
Good pointers to quality include thicker, more intracately moulded steel parts where you fit the wheels (the dropouts).
A sticker indicating the grade of material (chromly, butted, Reynolds, Columbus ...)
Budget for possible replacement of overhaul + replacement of bits that wear out.
I put together a very nice machine for that kind of budget.