Purchasing a car from CarMax

I found a car on their that I’m having transferred to my location (close enough that it is free). I expect it will be here for me to inspect and purchase within the week. I have two questions never having purchased at CarMax before…

1. Is there any negotiation on price? My understanding is that there is not.

2. Do I have to finance through them? Or can I seek out a loan through a credit union? I’ve never done the credit union route before, but I read another thread in here that recommended this to get a better rate. Curious to try it, but not sure where to start.

Any other thoughts or watch outs on this particular transaction and CarMax in general are appreciated!