First, some background: I'm a (former) mechanical engineer with a moderate degree of shop training and some metrology background. I also have been tuning skis for a couple decades, and know how to get "mirror finish" tunes at desired angles when I care to spend the time. I had recently taken a core shot to my Volkl Kendos, and weld/gun/iron repairs weren't holding. I therefore fixed the core shot for good with an inlay patch [*], and having done so I wanted to get the bases re-ground both to make everything flat and to put structure on the patch material.
To accomplish this I went to a ski shop in Mammoth that I trusted (Footloose, which is widely recognized as a first-tier establishment) and asked for a 1-degree base bevel and a grind [**], but no side-edge work.
The 20-something saleskid who took my order proceeded to lecture me about how I would ruin my skis by doing my own side-edge work, and how much more accurate their ceramic disk edger was than any hand tool (actually false. The ceramic edger is more productive and cost-effective for a high-volume shop, but it registers to the ski base in exactly the same way as a high-quality bevel guide and isn't intrinsically more accurate. It all comes down to operator skill either way). I basically had 4 options at that point
1. Go somewhere else
2. Debate the intricacies of edge-tuning with a salesperson (NB: this typically falls into the "don't argue with a pig" category of life experiences)
3. Ask said salesperson why a tuning rock-star like him was working sales during skiing hours instead of the back-shop at night.
4. Give in and let them do what they wanted, reasoning that the worst that couple possibly happen is that I'd be out $10 extra and have to polish out the side-edges afterwards as I'd originally planned.
Being a lazy sort of fellow I couldn't muster the energy for 1-3, and money isn't high on my list of priorities, so I went with 4 and asked for a full tune, with no detuning and 1/3 base angles.
Upon retrieving my skis, I observed the following:
1. They had indeed ground the skis and had hit the requested 1/3 angles, to the best of my ability to tell with my SVST bevel gauge. This is both the start and end of the good news.
2. The side-edges were a bit "wavy" as though the ski had wandered slightly on the edger base, though this was minor and I was able to easily polish it out with a 120-grit diamond file.
3. The bases were concave through the shovels. These skis had been flat after their previous grind. Typically this happens when the tech operating the grinder works a bit too fast and lets things overheat. Picture of one ski below:
4. The ceramic edger had bored "through" the right shovels on both skis just forward of the contact points. Ceramic edgers reference to the ski base, so what this means is that the tech running the ceramic edger worked from tail to tip on the right sides of the skis (not unusual for a right-handed tech), and failed to disengage them before the base "rose away", thus causing the disc to bore through the edge. See pictures below. The smooth finish to either side of the "ceramic disc hole" was applied by me, using a 120-280-400-800 grit diamond sequence. The original finish was much more striated in addition to having waves as noted above.
The bottom line is that this shop tune didn't even deliver what I really needed (a simple, flat stone-grind), and they took a bunch of edge life away by botching a side-edge sharpening job that I didn't really want at all. I estimate that getting rid of the concavity will cost about 20% of the base life of the ski, and filing out the divots in the shovels will take about 10-15% off of the side edges. I basically payed them $50 to steal $120 or so of pro-rated ski life, so my "net" is about minus $170. I claimed that I don't really care all that much about money above, but like everybody I have a threshold...
If you ski Mammoth and need a tune, I suggest Kittredge. Their somewhat arrogant attitude of years past seems to have been largely corrected, and their back-shop has always been well run. Footloose by contrast seems to have lost their way. They still have the best boot fitter in town (Corty Lawrence, the only person I would trust to cram my 98 mm wide knobby feet into a 96 mm plug-ish boot) and one other fitter (Craig I think - Short-ish, wiry guy with somewhat high voice and dark, curly hair) who's as good as anybody at the other shops. Other than that they seem to have decided to coast on pure attitude and good reputation. I actually feel sorry for Corty at this point.
[*] An inlay patch is where you use a template to cut out a regularly shaped piece of base material, create a matching piece of new sintered P-Tex, and glue it in with Hysol epoxy. I have a hot-box, so I typically cure for 4 hours at 55C/130F and then scrape the repair down after cooling.
[**] Most shops require you to get the base-edges bevelled at the same time as stone-grinding, because the bevel keeps the edges off of the stone and thereby allows them to go longer between dressings of the grinding stone. This is entirely normal and reasonable, provided that they do a good job of it.