From: Rabbi Moshe Sofer
To: Rabbi Meir
Rabbi Meir attributes to the Chasam Sofer a ruling against buying tzitzis from itinerant peddlers. The Chasam Sofer denies issuing this ruling, explaining that properly prepared tzitzis carry a presumption of expert manufacture. However, he cautions that traveling merchants are often unreliable and locally supervised products should be preferred when available.
Source: Shu"t Chasam Sofer OC §6