Let's mention my side of advance purchasing of day tickets:
Once I bought a CDR HFD to Brum New Street, with the intention of using it the next day, which I asked for. No problem there, but I could have got it the next day anyway. My plans changed at the last minute, so I got a refund, and had £3-ish left after.
Also, regarding the dumb ticket office staff, I concur they are not widespread, but you will get some that say a ticket does not exist when it does. The only similar experience I can share was buying a Swansea to Melksham SSR in January. The ticket office staff didn't know how to spell it, so I had to spell it out for them. That's as close to telling someone how to sell a ticket. I have more experiences of them not putting the right ticket stock in for a rover, which confuses the bus drivers big time. The only other time I can think of is when the staff initally refused to give me a FOR, wanting to give me a Saver First instead. This is not what I wanted, but I managed to persuade him to give it me after a bit of debate.
That's my ticketing experiences for now. Combo CDRs I've never had a problem with from here!