I know this person, a woman, who has a "recycled" circus dog. The dog is very good at doing tricks and in general at getting people's attention. But the relation she has with her dog (the dog is tiny and lives in a spacious flat with her) borders on the psychotic. When you meet her, the first thing she generally says to you as her dog scratches at your legs, is "look he's giving you a party". If you fail to properly greet the dog (it's kind of annoying if the dog scratches hard), she gets upset.

One day my mom had asked me to stay at her place for the day (to open the door for someone she was expecting), while she and that woman went off to do some important shopping. The woman's dog had to stay with me. Now my mom has a large enough garden, which I ushered the dog into. But all the dog did was go towards the front gate, sit there, and look in every direction, for hours, searching/waiting for her master.

Nonsense. It is important that the right type of dog be chosen of course. More than one is always good as well. A lot of the small dogs are really designed as  active  dogs (ratters). Farm dogs in urban environments are a nightmare: there's little worse you can do to a collie type than lock them up all alone in a house for ten hours a day.

On the other hand, hunting dogs were bred to put up with long periods of low activity so they don't get as worked up. For urban dogs, take a pair small hunting dog - say a dachshund - socialise them carefully, and you'll be fine. So long as you stick to dogs that still have a reasonable amount of sensible breeding in  them. Excessively bred show lines can be a nightmare. Having two makes sure that they're never left completely isolated from their pack.