Glad to hear they're moving in the right direction for you, but as Allen pointed out, you shouldn't accept an acid wash to fix this. We've seen this move a lot, and there's a good chance they're going to suggest it. No bueno. An acid wash doesn't magically remove "all the bad stuff" and leave the rest of your plaster alone. It chemically peels a layer of plaster off, and takes stains and imperfections along with it. Which looks good (but not always) and gets the builder and plaster guys on their way for the least amount of out-of-pocket for them. The original problem may or may not resurface, and the acid wash might be only a bandaid fix that will delay that reoccurrence until after your warranty expires. Which, again, is good for the builder, but not so good for you.
But that's the least of it. What will happen, whether the acid wash solves the cosmetic issues or not, is you'll end up with less plaster than you paid for, which means your finish is going to wear out that much sooner. Again, you won't realize that when it happens, it might be 10 years from now. But you'll very likely have to redo that finish some number of years sooner than you would have had to, and of course your warranty will be long gone by then. And worse, it's likely that that finish won't feel as nice, as acid washing etches the plaster. That's best case scenario. Worst case, a poorly performed acid wash can completely destroy the finish (ask me how I know!!)...
Hopefully they'll do the right thing, if not, you might have to stand your ground. Either way, listen to what they tell you, tell them you'll consider the option(s), and then bring it back here for TFP's take.