Sorry to hear about your bad luck. This kind of thing ticked me off from the start. I don't know if this helps for going forward but my

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IDK if the vendor will help or not. Who's to say it won't be crap again 3 orders from now.
I decided on mixing flavors with unflavored juice myself (DIY). I have decided that, with rare exception, I will get unflavored juice and favors in original containers (i.e. Lorann's in their bottles). Then I just mix it up to desired strength. I've done this because:
1) I ordered a flavor from a vendor and it ended up tasting like puke. Won't use it. Won't trade it. Must throw it out. Wasted $$. Their other flavors were good, though. So, WTF? The vendor probably mixed this flavor according to their recipe. Didn't work.
2) I ordered a caramel flavoring from a vendor for my DIY and it was just "watered down" flavoring (cut with pg). I can cut it myself. $10.00 for 10 ml and it was a rip-off.
So, I mix it up myself from Lorann's flavors (or use your favorite). I know you can't find every recipe this way... But I like my ry4 recipe better than some other "pre mixed" anyway.
Also, if I am sensitive to any flavoring, I usually know what is in my mix since I mixed it myself (recipes like Lorann's cinnamon roll are an exception... maybe its on their site).
If these sites/vendors are going to stay in business making juice, they must ensure quality and consistency. If you need for a juice to sit for a few days, they should tell you. I started this whole thing with a DIY kit because I could tell that this "coffee table" shop juice quality will vary widely.
If I where you, I'd get your flavors in the original containers from the flavor vendors where possible (Lorann's, PA, FA, others....) . If you have a flavor of juice that you "must have/try" and can find a recipe, get the components instead. Otherwise, order a SMALL sample from the vendor. But it's like you said, you ordered waffle before and it was great, next time, dish-soap. You can't tell.
There's so much variety in flavors by just having the components and mixing up a "recipe".... I try not to mess with that <insert vendors nifty-ifty flavor recipe here> crap much anymore. Exceptions are things that I think are fairly "pure" in flavor like a "Virginia tobacco" pre-mix nic that I will use as a base for other recipes. I have tried an RY4... meh.
P.S. Dram bottles like these:
https://www.lorannoils.com/c-6-super-strength-flavors-candy-oils.aspx - there are threads in the DIY forums on what flavors are OK to vape. Flavor never failed me. Some are stronger than others. Some threads say vapor production varies... but I've not had a problem. Real good flavors IMHO. I have some FA flavors that are quit good also.
Like I said, just
