If you find yourself paying too close attention to their drinks (number, sip frequency, amounts left, if it's a drink you've had or not, if they are about to take another sip now or not, speed of consumption, marks the drinks leave of the table, things people at other tables order, if their drinks are made well or not, the line of pretty bottles behind the bar) that's a red flag, and it's time to take care of something somewhere else.
If you hang out and enjoy their company and hardly notice the booze and are cautious about which safe drink is yours then a good time will be had by all.