had a weird moment at work

so today this customer came in and they were looking at all these products like they had never seen anything before. i mean it was obvious they were just trying to waste time, cause why else would you pick up everything? anyway, i was so annoyed that i just started telling them the prices out loud every time they picked something up, like a robot or whatever. after a while, they got all defensive and left. afterwards, i felt terrible but also wondered if it was better to be honest and frustrated or to keep smiling and pretend everything is fine? what's the right thing to do in customer service anyway?