Not to be sniffed at
Definition 1 of 1
Pro Tip 1/3Positive Aspects
Emphasizes positive qualities of something often overlooked or undervalued by others. 
A small apartment in this location is not to be sniffed at.
Pro Tip 2/3Polite Refusal
Used when politely rejecting negative comments or downplaying something good. 
She might not have experience, but her dedication is not to be sniffed at.
Pro Tip 3/3Slight Surprise
Indicates a mild surprise at the value or importance of something. 
This second-hand book sale is not to be sniffed at; I found rare editions!