I would guess that, generally speaking, it's OK, especially if you're just doing it with an 5K/day non- app checked account. Be nice with the API and don't poll it too frequently. Cache your results locally. Maybe use some of the Shopping API calls that are meant to check for item status updates. Platform Notifications might be even better for your use case. Definitely read the API license in full to make sure this is legit. I could be totally wrong about the above, as it's just my uninformed opinion.