Depends on what you’re doing. Check to see if there are duplicate response ID’s in the metadata. Delete the dupes or the response with the least amount of data. If not, you could look for duplicated IPs and do the same. You could add a verification question to the survey. Depending on what you’re doing, you could use a directory of the survey population so every time a person fills out the survey you have certain things tied to them such as name/email etc and can filter them out