I really have no choice but to cut my dog's nails myself. He's a good boy but even touching his nails sends him into a panic. He'll fidget and scream anytime the clipper gets close to his nails, but if I can distract him with food, he won't even notice when I cut them!
I have no idea why he acts this way, since neither I nor the vet (who used to cut his nails before) has ever cut too close to the quick. My theory is that either his previous owners accidentally cut his nails too short when he was a puppy and he never forgot it, or he's just making a big deal out of nothing I've heard similar stories from other chihuahua owners: misbehaving at nail clipping despite no previous injuries.
The vet used to cut his toenails whenever he went in for an appointment, but he just got more and more hysterical every time. I felt the stress was too much for him—not to mention my poor vet as well—, so I decided to do it at home.
What I do now is catch him when he's relaxed or sleeping and clip one or two nails a day, depending on how much he's willing to put up with. Then I always give him a treat and praise him, hoping he'll start associating nail clipping with a reward.
As for worrying about cutting into the quick.... I certainly do, every time. Maybe he catches my own stress! But I clip only the tip off each time, and if the nail is very long, I'll cut it over a period of days. It's easier for both of us to have very short grooming sessions than battle through one long one.