Friend of mine does freelance design and had almost the exact same thing happen. Client kept tacking on little tweaks, a logo here, some extra social graphics there, and never pushed back on any of it until the bill came. Turns out they assumed all of it was baked into the first number because nobody ever stopped and said "hey, this part costs extra." He told me the lesson was that once a client says "sounds good" without ever seeing a number, that's not really an approval, it's just them not reading carefully. So now he sends a quick "here's what that adds" email before doing any of it, even if it feels annoying. Costs him two minutes and saves him the whole fight later.

Checking the lab slip before opening the box won't help with shade issues. The slip just has the shade you wrote down, it can't tell you if the lab actually poured the right color. Real talk, the shade problem happens on their end when they pick the porcelain or stack the crown, not when they type in the order. What you should do is ask the lab to send a shade tab or a photo of the crown on the die before they ship it. Some labs will do that for free if you push back after a remake like this.