If you do get them tinted be sure to bring it to someone who is familiar with our style windows. When you open and close door they move 1/4". A good tinter will have doors open and trick computer to thinking they're closed to cover full glass. They also need to let it set overnight so that you don't have peeling issues a few months down the road from the windows going up and down immediately after the car is given back to you. At the very least drop it off to be performed first thing in the AM and pick it up in the evening if you have to. Otherwise get in writing that they'll honor their work after you've explained how the windows open with the door on your car.
Depending on where you are (I have no clue), there are different maximum tints for front and back, so if you want a uniform tint you may need to pick the front maximum (usually the lighter one). You also may want to look into what can be tinted. For example, some rules in China make tinting look idiotic since you have to leave a portion of the front doors untinted for the side mirrors. You also need to consider how much of the front can be tinted. Most tinters use a metallic (usually titanium) tint which is more lifetime than non-metallic (some of which are lifetime), but ask about this. Also be wary that some jurisdictions do NOT allow certain metallic tints due to their reflective profile. And lastly, if you think you may move to another jurisdiction, be aware that you may need to remove the tint if a smart cop notices your tint is too high for your new home. This isn't too likely, but can happen. Also during your regular inspection (again, jurisdiction dependent).
Your best first option is to ask the dealership who they recommend, and then use their cost/tint as a barometer of the locals. While a Kia dealership may not use the best, a Merc dealer is not going to send their clients to someone bad.
Don't be surprised if the tinting looks poorly done or has "bubbles" for the first few days. This is normal and will go away. If it doesn't then it was a bad job. And DO NOT go playing with the windows the first few days to check the quality. You should give it a few days to settle in so it doesn't peel. In fact, I wouldn't recommend opening them at all the first few days.
Lastly, take the sample at the shop into a bathroom and see if you can see okay out of it at night. Most are fine, but I have seen some that just aren't very safe for night driving, at least with my eyes.
Just a small update to tintlaws.com: that site was sold in 2013, the new owner failed to update it and many listings there are inaccurate (as i found out recently). So if interested, I recommend to check out this tint laws website for up-to-date tint laws.