Only the person who is actually paying for the event registration should have the registration units added to their Registration Fees tab. They should not also be added to their Guests' Registration Fees tab(s). This exact issue was addressed and already resolved in Blackbaud Online Express (https://kb.blackbaud.com/articles/Article/70096). It needs to be resolved in NetCommunity as well.
Yes! If you export event registrants and guests with their associated units, it looks like there are many more units sold than is actually the case. Also, if you pull the canned event income report, it inflates the amount of money because each of these guests are listed with the full value of the registration fee as unpaid. In a recent case, the report made it appear we had twice as much income from an event than we actually did.