The lore of the academy persuades as well. All sciences operate this way, building on the testimony of forerunners. The argument from authority is not decisive, of course, but gives weight. Science could not advance if all questions were reopened every five years. At higher levels of the mathematical sciences the appeal to symmetry takes a higher percentage of conviction.
Mere definition is a powerful argument, and is more powerful the more mathematical the talk.
Above all, there is analogy. That the Law of Demand is true for purchases of ice cream and movies, which no one would want to deny, makes it more persuasive also for gasoline. Analogy gives the law its majesty. If the law applied only to trivial items for which it has been 'proven' in modernist style, no one would care. That laboratory rats view cherry soda as a luxury good, though interesting, is not much of a basis for a human science.