The situation this addresses is common and expensive. A business decides it needs a new website, and the actual problem is that nobody can tell what it sells. A business asks for advertising, and the page it would point at does not convert. In both cases the requested work can be delivered competently, the invoice is fair, and the underlying problem is untouched. The business concludes that digital marketing does not work for its industry.
Being told early is uncomfortable and it is the cheapest version of the information. The same finding arrives eventually, either through a campaign that produces nothing or through a website that changes no numbers, and by then the money is spent and several months have passed. A disagreement in week one costs a conversation.
What that looks like in practice is a first meeting containing questions rather than proposals. What are you selling, who buys it, where has work come from so far, what happens after somebody contacts you. Those questions frequently establish that the requested work is not the priority, and saying so is the point rather than an obstacle to the engagement.
It also means occasionally recommending that you spend less, or nothing, or with somebody else. A business whose actual constraint is that it has no reviews does not need a website rebuild. One whose problem is pricing does not need advertising. Those recommendations cost revenue in the short term and they are the reason the advice is worth anything.
The disagreement is a position rather than an instruction. You know things about your business, your customers, and your market that nobody outside it does, and the correct outcome of a disagreement is frequently that the original request was right for reasons that were not initially obvious. What matters is that the reasoning is on the table rather than that one party defers.
Ask any provider what would make them tell a client to do less, because the answer separates people answerable to your outcome from people answerable to their own deliverable. Somebody who can describe a real situation where they advised against spending has separated the two. Somebody who cannot has never had to.
Expect it to be specific rather than contrarian. Disagreement that amounts to a general scepticism about what you want is not useful, and a provider who objects to everything is as unhelpful as one who agrees with everything. The version worth having names what the actual problem is and what would address it.
Then decide. It remains your business, and after hearing the argument you may proceed with the original plan. That is a legitimate outcome, and it is materially different from proceeding without having heard it.
Notice how the disagreement is delivered as well as whether it happens, because there is a version of this that is unhelpful. Somebody who tells you the plan is wrong without proposing what would be right has produced an obstacle rather than advice. The useful version names the actual problem and what addressing it would involve, which gives you something to decide about.
Recognise that this cuts both ways in a first year, since you will occasionally be told something is a bad idea when it is simply unfamiliar. Local knowledge, customer relationships, and an understanding of your own market are things you hold and an outside adviser does not, and the disagreement is worth having in both directions.