"It's a date."

Varric nods and holds out his hand because, casual (bordering on flip) as he's being about this, this is still a business deal and shaking hands is sort of traditional. Whether she accepted the job or not, he respected her cunning enough to treat her like every other person who worked for him or tried to take his money.

There was a lot of crossover between those two groups, so a standard of etiquette was important.