Some parts of marketing are about judging the bang for your buck and allocating finite resources among the various options. It sounds like that's what they wanted.

On the other hand, specific data about actual click-through rates, number of users, number of ad impressions, etc. would be required input to any reasonable approach for such judgement. Data, that is, not guesses. Estimates without ballpark cultural knowledge are also just guesses.

For my own part, never having bought Google ads, nor having displayed them, I would rather estimate no more than 1% of people would click on them no more than once per day. That's probably because I'm cynical about ads, use AdBlock, would rather rely on search and recommendation for finding products, and so do my peers. I don't have a good pool of knowledge for answering this question in a way that would be accurate, no matter what my estimation skills are.

You'll have hard data on your own products, but you can still only make guesses about your competitors' products, your complements, and other variables in the marketplace. Joining a company doesn't eliminate uncertainty, it just shifts the uncertainty from that company's numbers to everyone else's numbers.

Not really, not unless you're very small. People buy market research for a reason: data trumps guesses.

A lot of data is kept strictly confidential; unless there's a mole somewhere, a market research firm isn't going to have it. Many of these estimates are made by applying data that you know about your own company's operations to public information available about your competitors.