"I'll pay for it," Aziraphale said primly.
He was the one who had insisted Crowley actually buy some petrol, since the small, locally owned station was close to going under and the business could use 'a little boost.' The angel neglected to mention that he'd already instilled the idea in several people's minds that, if they were going to get petrol, they might as well go to that quaint little station run by that nice old couple.
So when the two arrived, the only empty place was the Full Service spot.
"You'd better," Crowley grumbled, pulling up into the opening and turning off the engine. "Over a hundred pence a litre is ridiculous."
"But didn't you have something to do with—?" Sensing the demon's glare under his sunglasses, Aziraphale decided some things ought not to be asked. Crowley had not been in a good mood all day.
"Nice car," the young attendant said.
Good, Aziraphale thought. Complementing the Bentley is always a nice—
"It's amazing she still runs," the man continued. "Don't think I've ever seen such an old car, 'cept at an auto show."
Aziraphale winced.
"Fill. It. Up." Crowley said between clenched teeth.
The young man looked like he was going to ask Four Star or Unleaded, but at an expressive glower from Crowley, the attendant saved his life by assuming Unleaded unless told otherwise.
The angel and demon sat in silence until it was time to pay. Seeing Aziraphale take out his cracked leather wallet, the attendant hurried over to the passenger side, relieved he wasn't going to have to interact with the man in sunglasses.
"I'm not sure how this is usually done…I've never been to a Full Service pump." Aziraphale carefully counted out his money and glanced over at Crowley, who was forcefully ignoring them. "Is ten percent the norm?" he asked.
The attendant smiled. "Ten to fifteen, yes, sir."
Aziraphale nodded and paid the boy.
"You two have a nice—"
Crowley screeched out of the station before the boy could finish.
Aziraphale sighed. "How much gratuity do you generally give?"
"I generally don't. Why?"
"Well, I asked the attendant—"
It was a good thing the Bentley was able to drive itself because Crowley turned to his passenger incredulously. "You tipped that brat?"
"Of course. Not everyone omits common court—"
"Nobody tips the gasman. No one. The station adds more pence to the cost of the petrol at the Full Service place. You're not supposed to give them extra."
"But he cleaned the windshield—"
"That's why they charge more."
"Oh. Drat." It wasn't so much that he'd given away the money, but that the boy had obviously taken advantage of him.
Crowley looked over at the angel, who had a slight frown on his face, and felt his mood lifting. He could tease Aziraphale for regretting his act of charity for days.