I've noticed that any custom player model I download and install is messed up. They all face the wrong way (upward and leftward). They fire this way, and it can be very confusing to see someone firing away from you but have them actually firing at you. Does anyone know what is wrong? How do I fix this?

If you downloaded models that are too old and from the previos version (1.0) then they won't work. Gotta get the new models.

I am using 1.0, so can the same problem be produced by 1.1--1.0 or 3.1-->1.0? I don't think any of my models had versions on them so not sure which version they can from.

Yeah, the same issue would arise from using 1.1 models in 1.0. Unfortunately, no one's really making 1.0 players. :( 1.1 weapon models will still work.