Ask HN: How do you deal with managers/customers questioning your estimates?

I suppose my own context is somewhat unique, in that we have a very technical product that's used by other technical products. This means our customers are all effectively engineers. Some of these customers even used to work on our product.

Whenever we tell them, for example, the team has estimated it'll take X weeks to do something, we continuously get pushback of: "Why would it possibly take so long? All you have to do is A, B and C!" (often providing incorrect solutions, increasing the burden of having to explain all possible implementation strategies to them and the risks involved with each step)

I've also experienced this in previous companies where managers, who used to be technical, do the same thing.

To me this is insanely disrespectful of the team, and it seems as though it's a boundary violation on some level.

Has anyone found a healthy, emotionally mature response to this line of questioning? Ideally one that results in the customer understanding that they're crossing a boundary of sorts here.

In an ideal world I'd much prefer to not have to give estimates in the first place, and rather involve our customers more frequently in our development process to help them see the progress. It's hard, however, to convince them of the value in this approach.