9 out of 10 times, railway staff have been able to issue rover or ranger tickets for me.
Two occasions where they haven't, one was a GWR ticket office who didn't know what a Heart Of Wessex ranger was, and couldn't find it on the system, and when I showed him the GWR Rovers and Rangers promotional booklet they've produced and HoW map of validity, he asked me which ranger on the map I wanted.
I gave up.
The second was a little more understandable, I wanted to buy a Dartmoor Sunday Rover from a GWR guard who doesn't operate in the Devon area. He did have codes for rovers/rangers within his areas though. I gave him the code and although he was grateful for the code, he couldn't find it on Avantix. However, the lady at Chippenham ticket office found it with no problem, despite saying she has never sold one before!
The third, I asked to buy a Heart Of Wessex Ranger on board a service to Weymouth. The guard couldn't find it and advised me to buy when I got to Weymouth.
Generally, I have had good experiences with GWR though, and have never had a problem with ATW.
IMO the most popular rovers and rangers should be made available on TVMs. Why the Devon ranger isn't available on TVMs in Devon still astounds me, considering its great value.