Big Power build?
There are competent people out there for the basic stuff, plus a few incompetent.
For Skyline side, there have been some around for 10+ years, like Rod Bell, RK, AMS, etc. who must be doing something right. Some newer people on the block. The 35, not yet got that sort of longevity but are getting there.
Fact is every tuner has a skeleton or two in the closet, they aren't perfect and sometimes it goes wrong. The true test of professionalism is how they respond to mistakes.
In the end, you want someone who does a reliable job, for a fair price and can be reasonably trusted - the key element. Clients by definition have to put a degree of trust in their 'tuner' and it leaves you wide open to abuse by those with an unscrupulous streak. Been there, done that, suffered the consequences.
I chose my GTR tuner based on how they conduct themselves on the Forum, through word of mouth and how they are when you speak to them.
Based on that, it's Litchfield and SRD for me. I'm not interested in World Records
SRD did my Supra for me, and it was stunning. Litchfield have a long history in tuning, and Iain portrays an air of professionalism and trustworthiness - now I'm not saying the others aren't trustworthy, just that Iain takes care of business with little fuss. Neither do the bashing and both have many returning customers. Good for me.
I always combine some other work with servicing, so I'm not travelling 300-400 mile round trips for just an oil change.