I actually complete most fake market purchases in less than 30 seconds, in part because the novelty of practicing my negotiation skills in Chinese wore off many years ago. The main trick is knowing what stuff actually costs... going in the evening also helps because the merchant doesn't have to bother with restocking (i.e. less actual work for them).

Anyway, let's take my Paul Smith polo shirts, the foundation of my summer wardrobe, for example. I've been buying them for 5 years and know that I can reliably pick them up for y30 (y25 is also possible, but those extra y5 can lead to me spending more than my precious 30 seconds, which I dislike). Anyway, so I say "30" and pretty much close my ears; works every time.... actually I paid y40 once a few months ago during one of those crack down phases, which lead to all but two vendors in Yaxiu taking a break from Paul Smith; having 10 stalls selling the exact same stuff is a beautiful thing for consumers.