Update: installer would not touch my valves, so I did it myself and it took ten minutes

I dealt with something similar when replacing the laundry setup in my basement last fall. The guy from the local home improvement place wanted to charge me an extra hundred dollars just to assess the water lines. He claimed the brass stop valves on my laundry hookup, which were standard quarter-turn valves, were heavily scaled from previous plumbing projects. I was skeptical too. I used a penetrating oil, like PB Blaster, on the ends of the valves and gave them a careful wiggle with a pair of channel locks. After a few minutes, they turned easily enough, which told me his concerns were mostly about protecting his own job rate and not my actual pipes.

I ended up spending my Saturday doing the disconnect myself. My washer, a Whirlpool, required the hoses to be tightened by hand, and then just a very gentle quarter turn with a wrench to secure them. The point is, when the issue is just mineral buildup and not a broken internal seal on the valve, you ussually just need a little encouragement from a penetrating spray. The profesional installers often try to scare you into paying for a specialized 'corrosion report' that you can handle in five minutes.

Next time, I figure I'll just bring a flashlight and a can of PB Blaster. It’s defintely not worth having someone tell you to wait three weeks while they get permission from a supervisor to give you a free assessment.

My situation was slightly diferent. When I installed my newer side-by-side dryer, the installer did bring up the stop valves, but they weren't talking about corrosion. They were concerned about the age of the plumbing and the type of fittings. My house was built in the late seventies and the existing stop valves were old galvanized brass. They pointed out that even if they could turn, the internal threads could be compromised after all those years of service. They suggested the risk of a pinhole leak was far greater than the risk of a simple blockage. I took thier advice, though I didn't like the idea of starting over. Instead of replacing the entire line, I had a local independent contractor come over. He confirmed the valves were mechanically functional, but he recommended using dielectric grease on the threads when disassembling them. That way, future attempts to turn them wouldn't cause any sticking or stress on the old components. It was a minor preventive measure.

So, while the delivery crew might just be looking for a way out, sometimes the warning from a professional isn't about immediate failure, but about long term integrity. Replacing fixtures is one thing, but if the feed itself is questionable, you're just inviting future headache.

Same experiance here, and yeah the second reply nailed it with the penetrating oil tip. When my old top-loader got swapped out, the installer took one look at the valves and said he couldn't touch them because of buildup. I went back an hour later and just worked them back and forth a few times with a rag for grip, no spray even needed. Freed right up. One thing I'd add: after I shut mine off, I ran the machine through a quick drain cycle before swapping hoses so there wasn't a bunch of water sitting in the lines when I unscrewed them. Made the whole job way less messy than I expected.

Gonna push back on the PB Blaster advice in the first reply. Spraying petroleum stuff around a valve that feeds your drinking and wash water seems like a bad trade for saving a few minutes of hand pressure. That crust is on the outside, it is not what is making the stem stiff, so the oil is not even doing much where it matters. Also not crazy about grabbing a valve body with channel locks and wiggling it. Old brass snaps, and if that stop is soldered on you can crack the joint and turn a five minute job into cutting open a wall. Just work the handle gently back and forth a bunch of times, it frees up on its own in my experience.