In buying an existing business you can have both positives and negatives it simply depends on the reputation of the business. Most of the books I read focused on you getting a good deal but this is not always the case as just because it is a going concern does not mean that it is any good.
The bank will value any going concern on two thirds for the building and about one third for the business you can haggle the business side down and I would do so as much as you can. The bank will only lend you money on the building side of the transaction as this is the only way they can get their money back should you go bust so be aware that you will need a bigger deposit than you would for a house.