I'd ask: "If this data is truly useful in a financial market context, why are you selling it instead investing with it yourself? What data are you collecting that you're not* selling?"
Because sometimes the data is useful when combined with other data you might not have yourself. Example: you have data on number of Netflix subs. That’s great. It would be even more useful if you combine that with Netflix churn data.
You can think of company analysis as a jigsaw puzzle. You may have a few pieces. That by itself isn’t useful unless u have the other pieces.
This works in theory, but in practice when you start making estimates of engagement numbers that are twice removed from the underlying stock price, you get into trouble. The deeper you get away from a direct relationship to stock price, the harder it is to predict something in practice.
What you're saying is correct but also puts a non-sophisticated seller in a poor negotiating position. They do not know what existing data the buyer uses or how their data can be complementary to anything.
I mean, I guess that's something that you can do but it's likely to get you laughed out of the room and greatly encourage them to reverse engineer whatever you were trying to sell.
If the data made a few dollars per thousand dollars traded, it would take you a long time to make meaningful income from it, as opposed to a market maker.
This is a good heuristic for the sale of trading strategies. If someone has a viable trading strategy, they should be raising capital or joining a prop shop instead of selling it.
But it's not maximally rational to trade on data instead of selling it if you don't have any experience trading.
And even if you're somehow able to figure out a trading strategy on this with no expertise, there are extremely few data sources that are actually proprietary so alpha decay is a very real thing.
I'd ask: "If this data is truly useful in a financial market context, why are you selling it instead investing with it yourself? What data are you collecting that you're not* selling?"