I looked at the Blueridgewoodshop Etsy shop and found this 1-3 lb mold:
https://www.etsy.com/listing/180820875/3-to1-lb-adjustable-soap-mold
It looks to be nicely made, and I can see now why he's doing what he's doing.
One thing I can't tell from the photos and want to confirm -- is the bottom just a square-edged piece of wood that just sits inside the walls of the mold? Or are there little tongues that stick out of the long sides of the bottom piece? If there are tongues, they will fit into grooves cut into the side pieces.
The first way will work fine if the side screws are firmly fastened so there is plenty of friction to hold the bottom in place. I can see why you might be uncomfortable with this design, but for a relatively small mold like this, this approach will work fine. Soap is heavy, yes, but not that heavy.
The second way is admittedly more secure, however, due to the tongue-and-groove construction that ensures the bottom will stay put. The tongue-and-groove would ensure the bottom board is properly located as well. The molds I made for my soap have this tongue-and-groove design. They come completely apart and that's nice when removing soap from the mold.
If you look at the 6 lb mold, he's gone to a different method of assembly -- looks like the long sides are permanently fastened to the bottom. This mold is too long to count on friction to hold a simple square-edged bottom in place, although a tongue-and-groove design would work for this mold too.
It's surely your call if you want to fasten the sides to the bottom, and I do think there's a lot to be said for peace of mind. I think it would be good if the seller showed a picture of the mold disassembled and explain the proper way to assemble the mold, so buyers know in advance what they are getting. That said, I don't think the seller is trying to pull the wool over anyone's eyes -- the molds will function properly as supplied, it's just not what you thought you were getting.