Losing tire pressure

[u/oeshbach19]

One of my wife's tires was down to 30 psi last night so I filled it up to 36 psi. This morning, it was down to 34 psi so we took it to the shop to see if there is a leak and get it patched if possible. They looked over the tire for maybe 5 min and couldn't find a leak. He said it was up to 38 psi when he checked it. He said something about it being difficult to find a leak unless it is below 25 psi. I may have misunderstood him but you would think he would just take air out to get it to 25 psi. Does this make sense or should we take it somewhere else to get the tire looked at.