The condition they provided was effectively "if you want to use GPLv3 you can use GPLv3". That's perfectly acceptable for GPL. What they are doing on top of this is saying "if you can't/don't want to use GPLv3 but meet some other conditions, we will dual license it under one of these other licenses for you".
Let's say I have an open source project under the GPLv3 which only contains a foo.txt.
"If you are creating an open source application under a license compatible with the GNU GPL license v3, you may use BrowserBox Pro under the terms of the GPLv3."
So I can merge the BrowserBox Pro under GPLv3 to become part of my project.
Now I remove the foo.txt and my project will be a BrowserBox Pro clone under GPLv3 without the commercial restriction.
IANAL, but I'm wondering if this license really is GPL3? Because it's like a modified version of it - "GPL3 with a condition". From there, that possibly non-GPL3 license says that you can "use" the software, but not redistribute it.
But anyway it sounds like he needs to decide what he wants, and that's probably a non-open source license, if he doesn't want commercial use.
The license for the project is not GPLv3 but if my project is GPLv3 then the non-GPLv3 license for the project grants me a GPLv3 license if I include it.
Which shows the problem with this specific license in a single sentence.
I think that's a little too reductive—foo.txt wasn't a real app.
Nonetheless, I agree with your broad point: that if somebody can use it under the GPL, they can redistribute it and then all those downstream users can use it under the GPL.
But I disagree there is anything to fix. It's copyleft FOSS but businesses are encouraged to buy a license. Everybody wins.
My suggestion would be to license it under the AGPLv3+ for everyone, and then continue to sell commercial licenses to anyone who wants an alternative to the AGPL. Most corporations will refuse to use that license even though they're allowed to (e.g., https://opensource.google/documentation/reference/using/agpl...) and it's 100% FOSS.
> if he wants his license to enforce being paid for commercial use.
Then it wouldn't be open source, so I am not rooting for that.
However, for better or worse, large successful businesses can be built on scaring companies to pay for a commercial proprietary license and/or support, for copyleft open source.
This should not be an issue.
The condition they provided was effectively "if you want to use GPLv3 you can use GPLv3". That's perfectly acceptable for GPL. What they are doing on top of this is saying "if you can't/don't want to use GPLv3 but meet some other conditions, we will dual license it under one of these other licenses for you".