Activity flagging and the idea of community moderation works fairly well, but there are always ways to improve it. Here are a few ideas to consider or where I feel the current system is lacking in some form:
1.) Reset people's ability to flag activities at midnight, local time. Currently, it is set up to reset 24 hours after the last flag was applied, which means you are always guessing when you will be allowed to flag another activity the next day. There is no indicator telling you whether or not you will be able to flag an activity until after you have gone through the entire process and try to submit it, only to find out that you are still temporarily blocked. This is a big waste of time. Just reset it at the same time every day so it is obvious. Another idea is to have some type of counter showing how many flags you have remaining in a day and/or when they will reset. A note when you apply a flag that states something like "You have 5 flags remaining today" and/or "Your flagging ability will reset at 8:00am EST on XX/XX/XXXX."
2.) Nominate or allow local ambassadors who have more liberal flagging limits or abilities. These people can be ones who submit an application and can be vetting by the location of the bulk of their activities over the past X number of years. This will greatly help to clean up segments if someone is willing AND ABLE to flag more than 5 or 10 activities at a time.
3.) Have a graduated limit to flags per day. The more active the person is on Strava, the more flags they are allowed. New members only get maybe 3 or 5 as a limit, but long-standing members get up to 100 (or whatever number works best). These limits can be reduced if it is shown that they are abusing the system, determined by a percentage of flags applied that get overruled or otherwise proven incorrect.