Swarmkeeper
Hero
For D&D 5e, I disagree. If a DM doesn't ask for a roll, the implication is that there is no meaningful consequence of failure. Could be that the shopkeeper is obviously telling the truth OR that it is impossible to tell that the shopkeeper is lying. If players wish to metagame that into meaning that the shopkeeper is telling the truth well.... they might be right or they might be wrong. They proceed from there at their PC's own risk.The problem is that if you don't ask (or allow for, depending on how you run it) a roll, you effectively are telling someone that it's impossible. If someone suspects a shopkeeper is lying and there's no insight check, players will then know that the shopkeeper is telling the truth.
It doesn't come up often, and I would never allow/ask for a roll for something that is obviously impossible. No matter how good your athletics score is, you can't jump over the moon. Unless you're a female minotaur because the cow ... well nah. Not even then.
That said, perhaps a more interesting resolution, IMO, is to come up with a meaningful consequence of failure. If the player declares an action with the goal of determining if the shopkeeper is telling the truth, the DM might then ask for a DC whatever# Wisdom ability check (with player choosing the appropriate skill, if they like). If the roll is a success, the DM will tell the player if the shopkeeper is telling the truth. If the roll is a failure, the DM perhaps will tell the player that it is not possible to determine if the shopkeeper is telling the truth AND the shopkeeper's attitude will also shift towards the hostile end of the spectrum.