How do founders use AI for market research and market sizing (TAM/SAM/SOM)?

Deep research modes can compile a documented market report in minutes, but unconstrained they produce confidently wrong top-down numbers by multiplying analyst headlines. Force a bottom-up build: tell the AI to size from buyer counts, pricing tiers and your actual segment, and to show every assumption with a source. Use the AI draft to find the right reports and data points, then verify the three numbers your pitch depends on by hand.

A quick orientation. The real value is below: resources worth your time, from people who've actually done it.