I have to disagree. As someone in the industry who has poured at hundreds of tastings, I personally find it quite rude to push your glass up when I'm pouring you a taste, as suggested here. In most events, I donate that wine and have no incentive to over-pour you a sample. More times than not, people are there to drink and are disappointed in the "sample" I give. Unless you rinse your glass thoroughly between each wine you taste, a "slight" sample blends with your previous sample. You need a solid few ounces in order to swirl it effectively, smell it, taste it, spit it, then maybe taste it again and dump it. Dump it. Nobody expects you to drink everything you are poured. Whatever you do, don’t push the glass up.