Okay so I feel better today. Here is the situation as it stands...
The yogurt place I go to changes its flavors quite often (the employee I asked today said about every 1-2 weeks), and almost all at once instead of a slow rotation. Essentially I went in today and found that out of the ~10 machines, about 7 had been changed out. This is not a bad thing because it helped me decide my strategy: I just need to remember what flavors I like and wait for them to come around again.
I took the "5 may be pushing it" comments to heart and only tried 3 this time - one I almost spit out (IMHO, "key lime pie" should NOT be that sour!

) but I loved the other two - georgia peach and salted carmel. Since they wouldn't go together well in the same bowl, I got peach and honeydew melon - an awesome flavor I discovered months ago and was psyched to see again. Next time I go (if I get back in time

) by I will get the salted carmel and mix it with my beloved butterscotch.

I have learned from trial and error that this chain seems to do well with fruit flavors, but the flavors they try and make that taste like "things" (i.e. mimicking other desserts like key lime pie, cake batter, etc.) never seem to taste right to me (usually too artificial). So I know better than to sample something I have tried before with the hopes that they improved the recipe.
Now that I know which flavors to avoid, future sampling can be minimized.

Also to the PP that asked about my prioritizing - yes you were being to literal - I limit my treat budget and therefore require justification to myself on any splurges outside of normal shopping. I am also on a budget that does not allow me the luxury of frivolously buying a yogurt I am less than thrilled with just to be polite.
I do not feel obligated to buy just because I sampled. I was more disappointed that I couldn't find something that I wanted to purchase, and curious what other people thought was a "reasonable" amount "allowed" by etiquette when it comes to sampling. I did not want to cross over the line into "taking advantage" territory, and after today I feel that I didn't and I know how to avoid it in the future.
@taffywduck - your story about the plums reminded me of the Simpsons episode where Lisa learns about the Commandment regarding stealing in Sunday School (Homer is stealing cable tv), and gets upset with her mom for eating grapes at the supermarket.
