An alternative to flat out saying no is to point out how expensive and risky what you've been asked would be, in terms of development time, maintenance, and other metrics that the business cares about. Even very rough estimates with a list of risks will usually do.

If somebody else comes out with a much lower estimate, ask them what they think about risk A, B, C... if you've got a point, this will usually work.

That's a bingo! It's never No! It's "Sure, this is what it entails and this is how much it costs". Especially if you're a contractor. If their willing to pay the price, why not take the money and do the work?

Mostly, I'd agree.

I have literally no idea how long it would take though, I couldn't in good faith put a number to it.

I also don't want the work - Windows isn't an environment I have experience in because it's an environment I don't want experience in. They wouldn't allow a rate change to do the work.

Jerry Weinberg had the Orange Juice test which always struck me as a practical approach to all requests.

https://medium.com/intercom-inside/the-orange-juice-test-c90...

If you do this, identify beforehand what you think is non-negotiable. Because it won't be a technical discussion, it will be a negotiation and you're liable to be committed at the end of it.

Of course, once you're holding certain things as non-negotiable... you're saying no.

This drives me crazy!

Dev: "It's a really bad idea, will take an indeterminate amount of time, and be a maintenance nightmare" PM: "Can I just get an estimate?"

I'm a big believer in pushing back on small words doing heavy lifting. "Just" is a big red flag in software delivery.

> ... it's difficult politically.

The thing to understand about politics is you can do everything right and still lose.

Here, the damage was already done by their unrealistic expectations. You were either going to accept the job, fail and make them angry, or reject it and make them angry.

Sometimes your least worst option is to cut your losses.

Ok cool but if they have to deliver it, they’ll look like fools in the long run when they can’t, and in the end they’ll see you’re right? So it’s a win for your reputation in the long term I think?

My guess is no one will look back and say "Huh, he was right".

The only thing that probably is going to happen is "Huh, why isn't that delivered?" and then they will look everywhere but on the fact that it was, at least partially, just a stupid idea in the first place.

Of course I don't know the exact situation so it's more of a thought on what happens in general in the industry.

At the risk of a totally uncalled-for derail into politics - this is a hilariously apt description of Brexit. It makes me want to reanalyze the entire situation from a project-management perspective. It suggests a possibly illuminating metaphor: party leaders = management + sales, the electorate = the customer, and representatives = developers and engineers.

That's naive.

Nobody will revisit the GP's reputation, and after the novice devs fail to do the work people will just scatter into different projects. They may or may not take a reputation hit, while the PM that insists so much on doing the not viable work will take none of it.