Issues with an artist I hired for a freelance project

I'd like to repeat what Manta-Talmantas said. There is no real difference, at the basic level between rigging in Max and Maya. In fact, Maya rigged characters easily transfer to Max, and visa-versa. I'm not sure that your experiences with "great" incompatibilities between Max and Maya hold up in this context. In general, Autodesk has made great strides in erasing differences between Max and Maya over the last several versions. Maya does have a more sophisticated rigging and skinning apparatus. It is easier to develop a rig (more quickly) and the skinning tools can create a more sophisticated and elaborated rig than MAX. But this stuff is for advanced character design - probably beyond what you requested, so the difference is moot. I have both Max and Maya, and generally prefer Maya because it is easier and quicker. A preference for Maya should not set off red flags for you, especially since you want an FBX file as the final product.

However, other things that you are reporting do seem questionable. But, your moeny will not go to the modeller if you are unsatisfied and the money will be returned to you.

The rig doesn't need any specific game engine features, it just needs to use bones and have the specific bones I requested. I don't know if he doesn't use Max, he didn't specify. He showed me samples of his rigging work, and it looked decent enough to pay him for the project.

Its now been several days since I gave him permission to use Maya, and he hasn't responded. It would have been nice if the project system allowed you to pay an artist AFTER they completed the work, instead of before. Paying someone before they do something is a foolish and stupid way to run a business. Now my money is locked up in the CGtrader system, with no way for me to reclaim it and give the project to someone else.

I'm basically stuck waiting for a response from this guy, hoping he actually finishes the project.

If the end product isn't what you asked for, you can just contact support for a refund.

Btw, its not exactly clear what you mean by standard rig. For instance some game engines require specific structure and naming of rig, and these standards may wary from engine to engine.

I have no idea on general situation here, but as far as i understand standard joints in maya are the same as bones in max. Unless you use scripts and all sorts of things.. so if one would rig a char. In maya and export it as fbx there shold be no problems. Though it is indeed weird one cannot do it in max. Might be he just doesnt know max?