Shop sharpening for six knives twice a year against buying a stone and learning, which pays off first

The variable nobody prices is how much steel comes off. A belt system in the hands of someone doing forty knives an hour is fast because it is aggressive, and aggressive means your knife gets measurably narrower every visit. On a knife you paid twenty for, who cares. On anything with a nice profile or a thin tip, three or four of those visits will visibly change the shape of the blade and you will end up with a knife that no longer sits flat on the board. Ask what machine they use, and if the answer is a fast belt with no mention of a jig, take the cheap knives there and nothing else.

Run it as a comparison rather than a price. A decent combination stone plus a cheap angle guide costs somewhere around what two or three rounds of shop sharpening for six knives costs, and the stone does not run out. So on pure money the stone wins inside two years and then keeps winning for a decade. The catch is that the first two or three knives you do will come out worse than the shop would have managed, so if you go that way, learn on the four you never use. The two you care about get their turn once you can raise a burr along the whole edge without thinking about it.

I did the cheap while you wait option for years and told myself it was fine because the knives cut afterwards. What it cost me was the profile on my only good knife, slowly, over about five visits, and I did not notice until I put it next to a friend's identical one. That is not an argument against paid sharpening, it is an argument against the fastest cheapest version of it.

I use both and split them by knife. Everyday stuff, bread knife, the serrated things, the knife I let guests use, all go to a service because I do not want to spend my Sunday on them. The gyuto and the petty I do myself, because they need a specific angle and I would rather control it. Mail in services that specialise are genuinely good, they will fix chips and reset a bevel properly, but you pay for that and you lose the knife for a week or two, so it is a once a year thing not a maintenance routine.

Two knives that matter means one stone and twenty minutes of learning. Anything you would not miss can go to the shop forever.