Is there a limit as to how often checks are performed?

We run our checks based on when our APIs are being called, it is completely customisable which actions are sent to our system and which APIs called during the requests. 

However it is recommended for certain APIs to be called only during specific actions to optimise the performance and costs. 

For example the Email API is suggested to be called when a user enters or edits the email address, on later connected transactions the enriched results would still be presented. 

Regarding QPS (Queries per second) limitations, it is set at 2QPS during the trial which is increased to 10QPS or more depending on your needs.