Worried bartender is still in a childs mindset; ask those guys where they work
I tended bar for almost a decade and made great money, drinking isn't my first choice but those two bartenders were dropping $50-60 bucks a day on a drink and a tip...those bartenders might be walking away with a a couple hundred to thousand a night and are just supporting the young, naive bartender knowing how many people will stiff'em and they might come to his bar because its cheap, meaning our 27 year old pal isn't getting a high gross unless there is insane volume, which 2 beers and 2 shots for $30 is pretty mid in my neck of the woods, you can find better deals but I've also worked places where 2 beers, 2 shots is $45+ because of the liquor being sold.
Next time they come in find out where those bartenders are working, be a little curious and find out if the money is good. Also if they keep tipping you, throw them an extra shot or free beer or pour everything as they come in just out of respect for throwing bones your way.