This is from the satirical Private Eye magazine, but in their submissions column so I guess this is a real quote. Makes sense to me.

“Our sniffer dogs are very good at finding drugs,” a police spokesman told reporters at the airport in New Delhi, “but they’re no good at identifying exactly what it is that they’ve found. Drugs sold on the streets, like hash and heroin, are often mixed with anything from boot polish to cat litter, and although we can usually detect opium by the smell, we often have no idea what we’re dealing with. Laboratory tests take several days, and portable testing kits are unreliable, so when we need to know immediately what the substance is, that’s when we call in the tasters. It may seem unconventional, but addicts are experts in their field, so why not take advantage of their skills? We go to particular slums, depending on what we think the drug is, let the local junkies sample our find, and pay them a fee for their opinion. For official purposes, we then send it off to the laboratory for analysis, but there’s no need, because the tasters are never wrong. They always know if we’re dealing with the real thing, and can always tell what it’s been cut with."