Capability is top on this list to select a calibrator to tune your vehicle. Selecting a tuner that knows your particular vehicle and modifications will give you more confidence in your build. Seeing previous customers cars or talking with the tuner will get you more information on how knowledgeable they are.
Each tuner will have a speciality. Is that speciality your particular vehicle? Tuning every platform is not having a speciality. You may want to pick someone with more knowledge in your platform so if parts are needed they know the proper brands and parts to pick. Attention to detail is key, and to know every platform is not realistic. Anyone can get by on a tune, but is it what you are needing for your build?
Aggressiveness is a concern for most customers. Not every tuner tunes for the same results. Tuners may have the drive to have the fastest cars but aren't concerned about your wallet or engines stability. Some tuners focus on keeping a vehicle at a conservative tune for less likely of engine failure to happen but still perform at optimum levels .
Drivability is a main concern for some tuners as well. How well the car actually drives, and maintaining some fuel economy is what most customers do think about even though it is a performance vehicle. Tuning for peak power is simple, it's the details in the drive-ability that count for most people, and not every tuner will focus on this. It takes more time and knowledge in tuning to perfect this.
Availability: Is this tuner available when you need him/her to be? Are you a ONE and DONE customer where availability doesn't matter because you just need them one time. Or do you need this tuner on a weekly basis checking out data-logs for an event you are attending? If you change parts often where retunes are needed monthly, this may be something you need to discuss. Knowing the tuner is available to come out to your events is also an advantage in selecting a tuner.
Being available to look over data logs remotely is also a benefit. Does this person have the skill to tune remotely?
Tuning your car doesn't stop at the dyno or street, things may pop up that you notice from your own driving style that needs adjustments. Being available to do test drives and make adjustments will prove your money was well spent.
Communication is a large factor for many customers. If the tuner can't communicate what needs to be done, or if anything stands out during the tune, how will you know where your build stands? The more questions a tuner asks about your build, the better. They want to understand what you do with the car, and what you will need to properly get to your goals. Just because the internet or forums told you can, does not mean you should. Listen to the people who do this on a daily basis, and their reasoning for it. Valid points will be brought up here if there are issues.
Can this tuner grow with your build? Basic bolt on modifications or stock applications require less tuning skills than a build with forced induction or alternate fueling. If you know your build will progress, can the tuner support your build? Some applications will require standalone ECUs to better tune your vehicle over the stock ECU. Are they only capable on one tuning software or multiple? How advanced are they in tuning different softwares? For most customers this won't matter but if you are a racer or looking to build 1000+HP builds, it is something to consider.
No, this is not a sexual chemistry, this is customer chemistry. Do you get along with this person? You might have to have a closer relationship than you think. Late night calls, understanding directions, and listening to the professional opinion of this person does matter. When he or she gives you their opinion on the build or tune, you should listen and consider this for the safety of your build.
Pricing isn't a big concern for some, but it is for most people. Even though pricing shouldn't really matter when it comes with the proper knowledge and availability, but this will always be on someones list of priorities. When searching for a tuner for your vehicle, consider the after sales as well. How will things be handled if adjustments are needing to be made? Someone with a lesser cost may not give you the attention you are needing to get your car dialed in.
Location is another one not high on my list, but it is for the average consumer. It is convenient to have your tuner close to where you live, but you can't always count on that. Some may drive hours, or work with someone remotely in another state or another country because you know that tuner will give you what you are looking for.