I feel like some people still have a misconception of how Mare functioned.
Normally, to see another player's character in all its gooner-modded glory, you need to sync up with them by giving them your personal Mare code and receiving theirs. They scam you and only receive your code without giving one back? Nothing happens since you did not sync with theirs. If you are also not completely retarded you can set a maximum file size that Mare is gonna download, so you could prevent zipbombs that way.
Now, since people are generally retarded, you could also create and join something called a Syncshell (haha, get it, it's like a linkshell but for syncing with Mare). Everyone inside a Syncshell will automatically share codes so to speak and download character data from everyone in there as soon as you get into the same map or instance. Just so you get an idea of the file sizes for mod beasts, they usually start around 400-500 mb if they are well compressed, but easily go up to 1.2 or more gb. And that's the file size without any additional animations or VFX.