My general rule of thumb is to order "as is", at our nicotine and pg/vg levels, the first time ordering from a vendor - no extra flavor or "flavor shots". If we like the flavor enough to order it again, but think it is a little weak, then we may order extra flavor. So far, this has served us well.
One of my daughter's favorite eliquids when we were using cigalikes was Mt. Baker Vapor's Hawk Sauce. Since we started using Evods and Evod Glass, she has found something lacking. We were using the Evod Glass with Kanger single coils. I just had to order her a couple of new tanks - she works, does all the shopping, etc., so her tanks take a beating. She decided to use the dual coils that came with the new Evod Glass tanks, and she really likes the flavor she gets with the Evod dual coils with other eliquids that we have on hand. She is planning to try the Hawk Sauce with the dual coils before we make any decisions about getting extra flavoring to add to what she has on hand, or ordering Hawk Sauce with an extra flavor shot or two.
What you get and what you expect from different flavors can vary depending on how you perceive the taste with the equipment you use, whether you steep your eliquid, etc. We are quite willing to play around with Hawk Sauce, since we know what made my daughter fall in love with it, and use it as her "go to" eliquid when she was stressed out. If you start out with extra flavoring, and you do not like the eliquid, you will have no idea if it is the extra flavoring or the flavor itself that you do not care for with the equipment that you are using. At least if you start out without extra flavoring, you will have a better idea if you are looking for more flavor or if the eliquid is just not what you are looking for.