Could postcards with scratch and sniff actually be useful here? If you just ask people about their sense of smell, I'm not sure they can give you a reliable an

Could postcards with scratch and sniff actually be useful here? If you just ask people about their sense of smell, I'm not sure they can give you a reliable answer. But maybe you could design a postcard to give them with a few numbered squares on it, and they could tell you whether they notice anything when they scratch each one of those. (It could be a blind test, too.) Stick a URL or QR code on the postcard and you can collect the data. The postcard could serve as both material for the experiment and advertisement. Mail them out to random people in an area you want to sample. I've gotten these sorts of things in the mail as advertisements in the past, so obviously it's very feasible to produce them.