1. Bots don't make purchases (and you can't identify them anyway), so there's nothing to take the costs off of.
2. Again, no way to identify users (bots use hordes of residential proxies with only a few requests per IP).
3. Agents and bots care more about a universal solution that works for all the sites than an efficient solution. You could standardize on a header for this, but then some sites would start hiding some content in the API for "business reasons", making this header untrustworthy. Unless you're a site so large that it deserves special handling, it ain't gonna work.
2. Again, no way to identify users (bots use hordes of residential proxies with only a few requests per IP).
3. Agents and bots care more about a universal solution that works for all the sites than an efficient solution. You could standardize on a header for this, but then some sites would start hiding some content in the API for "business reasons", making this header untrustworthy. Unless you're a site so large that it deserves special handling, it ain't gonna work.