your dialogue flows really naturally! i could see—well, hear—a conversation like this happening in real life. the characters also seem to have chemistry, and i think it’s cool you managed to convey that in just a few lines of dialogue.
i’m not sure which tense your excerpt is intended to be in, though. e.g. you say “whispered to Roza” in the first line and “She whispers back” in the next. the tense has to be consistent.
but yeah overall good dialogue. it’s witty and shows the characters’ relationship with each other well. 9/10
Taking a last look at the clear blue sky, Foster sat down in the backseat beside a gentleman whose knees almost met the seat in front of him. He was extraordinarily tall, with dark, brooding eyes—exactly the kind of person Foster expected to find in the backseat of a mysterious car. “Hi,” he said, extending a hand. “I’m Foster.”
Beginning at Foster’s unruly strawberry curls, the stranger sized him up. He was underdressed. Both the driver and passenger wore suits and ties, making him uncomfortably cognizant of the fact that the buttons on his Hawaiian shirt weren’t all lined up. Probably deciding Foster wasn’t a threat, the stranger finally shook his hand. “Ross,” he said, but that was all he said.
“So, uh—“ Foster pushed his glasses back onto the bridge of his nose. “—where are we going?”
For no more than a second or two, Ross’s dark eyes settled on Foster, then returned to the passing landscape. “A crash site.”
“A crash site,” Foster repeated, nodding slowly. “What crash site?”
“It’s an experimental airplane.”
“Well, was an experimental airplane,” Foster said under his breath. He smiled a little, but Ross did not. After that he couldn’t bring himself to look at the stranger again.