Main points to consider: see the dentist's previous work. This is a must. Also, ask about the temporary teeth you'll need to wear before the permanent ones are crafted and arrive, which is possibly a month or more after the initial grinding down of your real teeth is done. The factors that go into good veneers are the dentists sense of artistry, skill, the quality of laboratory that actually makes the veneers, and the dentist's concern over the temporary teeth you'll need to wear while the final veneers are being crafted.
To be sure, the grinding process is the toughest and longest part involved in getting veneers. For four teeth, I spent almost five hours in the chair while the dentist is grinding and making temporaries, which is a multi-step process. My dentist paid special attention to the temporary set, which many don't, so one doesn't show up for work later with totally fake-looking teeth. I'm very pleased and happy I did it. No problems, no complications, just beautiful.
By the way, I earn a moderate income and I'm no celebrity, just tired of being embarrassed by stained teeth. Each one cost $1200, but they are mine forever. I wear a nightguard to ensure they remain safe.