You may think that bartenders are not in the business of sales, but that is untrue! For the bartender who thinks in dollar signs, this means the more sales, the more tips.
Before you start your shift, you may want to agree upon the specials and be thinking of how you can suggest them to your customers. If your bar serves food, you'll want to be familiar with the menu so that you can recommend dishes that pair well with the drinks your customer's order. Perhaps you suggest top-shelf instead of well.
"I am great with upselling my customers or pushing the latest specials. If a customer asks for an IPA, and we have a similar local craft brew available, I will suggest that they try it. Local craft pints sell at our bar for an additional $1.50 which adds up at the end of the day!"
Entry Level answer example
"I think that the best way to upsell as a bartender would be to recommend a cocktail before the wine and food are delivered to the table. This upsell technique would require a strong knowledge of the menu."
Experienced answer example
"To upsell, I always recommend top-shelf liquor. We have a lot of gin drinkers in my current establishment. We sell the well gin for $4/shot, and it's Gordon's gin. We also sell Hendricks gin for $8/shot. I have a few of our regulars hooked on Hendricks, soda, and a slice of cucumber. Some people prefer the unique taste and find the small splurge to be quite nice."