These are some samples of 3/4 inch marine fir, meranti and okoume:
A few things you notice are the number of plys.........7 for the fir, even though it is marine grade.......13 for the other two. Even though the fir was marine grade, it has a number of voids in the plys and checks checks in the faces. In one instance, I counted 13 footballs in one 2' x 4' section. That was for fir from 10 years ago. The current stuff is much worse.
The meranti and okoume have not had the issue with voids.....or at least the stuff I have used in the past have not. An interesting thing happened with this sample of okoume..........again, it is 3/4 inch and appears to have been made by glueing up two 3/8' panels. Not what you would expect to see. Bottom line is with the declining quality of everything, there are no iron clad assurances of anything. Others may chime in, but a good indication of quality may be the price. If something looks too good to be true, it probably is.........and that may mean some cheap, inferior stuff that is not what you thought you were getting.
Second photo is of the same pieces of plywood........these had some oil applied to give an indication of the color if finished bright:
Again, from left to right........fir, meranti and okoume. I don't think the normal meranti will finish as dark as this appears. It is lighter than walnut. Okoume does seem to have a pinkish tint to it.