Currently doing a commission for a guy, but I feel slightly suspicious about them because of their intermittent lack of activity and the fact that they “restarted the discord server” for no apparent reason.
Luckily however, most of my build is made up of meshes. Therefore, if they synapse the game, will the meshes be able to load or has mesh privacy been added?
Meshes I believe are public if they have the ID to it so even if it’s not on, for example, the Creator Marketplace it will still be able to be used if they have the Mesh ID so if you send a file with mesh then yes the meshes will load. I am not sure if they load with Synapse I believe they do.
Although I believe there is a way you can “archive” the meshes. Although you’d have to look in to that yourself.
Just don’t allow them to join the game. Take as many screenshots as you can.
Well, if you don’t trust them, make your inventory private, build on your own game, make the game private and only show the game to them with screenshots, screen recordings or through screen share and only hand off the place file after you’ve been paid.
When a player loads in a mesh object, the mesh and texture ID is loaded in along with it because the game needs to know what to actually show on the screen, so yes, if for some reason someone does use any exploit to steal your map and is successful in doing so, the meshes will be copied too.
If this has already happened or if it does happen in the future you can archive the meshes as others have mentioned:
go to your meshes, find the stolen mesh, press the gear icon and click “Configure”
After that, scroll down, and click archive.
That’s about the only way you can “100% guarantee” that they won’t steal the place or your assets.
Note: Maybe you don’t trust someone so much then maybe its not the best idea to work for them 
I hope this helped.
Good luck.
