Data is obtained from companies such as opta stats. The club would simply be agreeing KPIs for particular positions and using the results to vet transfer targets.
I would expect this to be the case. A subscription to an existing service would be far more sensible than trying to build your own model from scratch, as that's a huge undertaking that would, frankly, be beyond our means. Of course, that doesn't afford you a competitive advantage as you only have access to the same pool of data as every other subscriber, but that's the trade-off you always have to make in a buy vs build selection process.