I don't think it really matters if it's old line or they just put it on yesterday. Most of the time they fill it with as cheap a line as they possibly can. Just another way of saving money. When I get a new reel with line already on it, I leave just enough of the old line for backing. A good rule of thumb is to measure out your longest cast and add 25-35 feet. I cut off the original line and discard it and the tie a uniknot to the line I prefer using. I keep several big spools at home because it saves me money.
Line is never a good place to try to pinch a penny. Much better experience fishing with line that gets the job done. I invest to much in each trip for gas, food, time, and effort, etc. to take a chance on ruining a trip with lousy line. How you prefer to fish and what tackle you will be using will determine what line will work best for you. Just because it performs well for somebody else, it might not do the job for you if you're fishing with a different setup.