Mostly I've done them myself, only take them to a hydraulic shop if I can't handle it. Biggest challenge is dismantling without a proper fixture. A real shop will have equipment to turn big high torque nuts & tricky gland plugs. My Case backhoes have only two holes in the face of the gland, uses a special spanner. First boom cylinder we did, it was a homemade spanner with a ten foot handle. Took me & Seth all day to free it. We had to use heat, a smoky, messy process. These have about a 6" long fine thread. We got it out a way & it had red Loctite. Miserable job. Different backhoe, same boom cylinder, I believe it had been shot. Looked like a bullet dented the barrel of the cylinder. I took it to a faraway hydraulic shop. they built a new barrel & piston, cost $1300.
Another cylinder, stabilizer cylinder in this case, we rattled on the piston bolt with a 1" impact wrench an hour, couldn't make it budge. I took it to the same hydraulic shop. They had a hydraulic "wrench". Broke three Chinese sockets before explaining the old owner took much of his tooling with him.
Hydraulic shop in Eastern New York State, I called the Case dealer in Western New Hampshire, 100 miles away. The service manager said "Get it here by 4:00, we'll do it today. I rolled in about 4:06, 5:55 I was on my way home with a rebuilt cylinder with a wet coat of paint. If I recall it cost about $250. for them to seal it. I had bought the seal kit from them earlier.