If I were an NPC, I'd want a player character instead of a dog. They sleep and eat elsewhere (or not at all), don't need to be taken for a walk (just give them a goblin to play with), they are not smelly (even if they just crossed a swamp full of undead hydrae) and all you got to do is giving them some coin (which a game designer placed in your inventory) when they solved the task you gave them. Sometimes you can even send them to someone else for payment. You may even tell them you tricked them into work and refuse payment 'cause you are oh-so-terribly poor. As long as you don't withhold their experience points, they won't even eat your brains. All in all, they make marvellous pets.
Though, pets can be quite unnerving if they do the same all day. Dogs retrieve sticks you throw for them. Player characters retrieve stolen jewellry, your ancient family heirloom, or just a random number of, well, sticks. So what if you want a more interesting pet? Tell him so save the world? That's crap, you'll just get killed by the evil guy to motivate the player character. But there are different kinds of tasks to send them off with and still survive.
For an instance, send them off, then disappear into nothingness and leave the payment trouble to someone else. Your opponent in a certain quest, at best. The only important thing is not to leave them without a quest solution; they would pursue you and get your purse or your head, or both.
You're on the secure side when you just hint the quest stuff as a rumour to the player. Make them get you a bottle of good old wine, have a nice drink and rant drunkenly about that treasure hidden in some old ruin or in the house of another NPC whom you would wish some decent thieving. Even if this is not the whole task, it's a good start: When players need to do something beforehand to get the real quest, when they do something and find out there's more behind (like a dump of rotting corpses in the basement of the NPC's manor) they're more likely to run after the stick you throw them.
Sometimes you can even get money from them. Put on the worst set of clothes in the game, wait by the roadside and whine about them evil robbers in the woods, or the baron who threw you out of your house. Money is only the usual part, of course. The true worth in this kind of quest is not the gold, but the fun when they slay the robbers or the baron, or get themselves some bruises while trying.
The annoying part is that you'll never get the really cool items which the player loots from their foes. Players always keep the good amulets and swords; if not, they'll be pissed. So make them choose: The item they are to fetch, or a good deal of money instead; or a different item. Whatever they take, they will feel it's worth even more as is truly is, as they choose and paid. It might get even more worthy when they have to do something evil to gain it. Truly evil. Others must loathe them for the deed, and not talk and trade with them any more.
Always a nice distraction are curses. Be it a cursed object which they shall find - or which they stumbled upon, what a coincidence! - or a curse which their opponent in the quest lays on them; it gives you a good reason to get them rid of the object and claim it for yourself. Still, they fulfilled the quest. Most likely, they needed the cursed weapon to do something awful which you didn't want to stain your own hands with, but you'll look like the nice helpful NPC until you're off with the amulet / sword / handkerchief of doom.
The most amusing and most content player character pets are those who never notice being pets at all. In the end you can even decide to let them know they've been a nice dog. But then, keep in mind you're an NPC, and worth some experience points if they want to whack you with their newly gained weapon.
More new rants on my blog. dracoliche.blogspot.de/