I have always done them as a vertical shop, as I did with their predecessor. Not once have I been admonished that they were done vertically. Of course, I always rotate them whilst at the station after downloading them into my laptop.
My greatest problem has always been getting the straight-on shot - there always seems to be one vehicle with their driver dawdling at the pump. Many times they seem to be looking at their smartphone, talking or texting.
As usual, I get back in my own auto and drive up behind them, waiting patiently for them to drive away. Just yesterday I did this and the driver came out from the convenience store looking panic-stricken as I was writing on my cheatsheet that was attached to a clipboard.
"Are you an undercover cop? Is there something wrong with my truck? Have I done something wrong?" he asked.
"No," I calmly said, smiling nicely. "I'm only doing an audit for the company."
"Oh."