I was only half kidding when I said that. If the tea is a dud, you'll pretty much know right away. If it's good enough to consider stocking, numerous sessions are required to determine where it really stands.
How often have you tried a tea and said "Fantastic!", only to be less than thrilled the next time around. Conversely, I've been unimpressed with a sample the first time, then learned how to get the most out of it and ended up enjoying it. By the time you get fully comfortable with a tea, you may be well into the cake, so it really is just a big sample after all.