There are good and bad landlords, and good and bad tenants.
We count ourselves as good tenants, and we like to think we're pretty good at finding good landlords. I find it's about taking your time when you look around the house, checking that everything works, looking for any signs that the house has been neglected, asking questions, and generally talking to the person who owns it. (We have rented through agents before, but wouldn't do it again because we're much happier dealing directly with the person who actually has an interest in making sure the property's looked after.)
We currently live in a lovely house that was immaculate when we moved in because the last tenants had trashed it (and stolen the kitchen appliances when they left), so our landlord had had to repair the damage and get it totally redecorated. We pay the rent in cash every month, which is good for our landlord because it gives him an excuse to come round and reassure himself that we're looking after the place, and good for us because he always checks with us that there aren't any problems - there haven't been any other than a leaky seal around a bath that we sorted ourselves. We've been here a year and he's just offered us a new 3 year contract, which is great for us because we know he really wants to sell the house if the market ever picks up, and we'd really like to stay here!
We're still friends with our last landlords - we only moved because we decided we wanted to live nearer the coast. And our landlord before that was so hands off that the only time we saw him in nearly 3 years was when a washer went on the kitchen tap and we couldn't find the stopcock - he was round within 5 minutes of our call.
There are exceptions to the rule, but I think if you're good tenants, you'll generally find landlords who look after you. Unfortunately, it doesn't seem to work the other way round, as our current landlord experienced before we came along.