I started buying oud midway through 2018 I believe, and not wanting to commit to full bottles and to experience a multitude of different oils from different regions and price points I bought a
lot of samples.
Agar Aura ones were the worst, they were offered in plastic vials for 0.15g I believe. The oils in these turned completely solid and the fragrance was almost non-existant. I did buy other samples from Taha last year and they were sent in glass vials, which were much better.
But yeah everything
@Mr.P has said rings true. If you buy samples then please use them up. I need to heed his advice regarding adding ethanol.
BTW I take responsibility for buying too much and not using them up. A while ago I realised how many "close to empty" samples I had and began to use them - which meant actually overapplying like crazy. I have several oils from ASO which I've yet to use, they were 0.2g IIRC and I seem to have gotten 10 or so "wears" from a single one. Multiply by that by owning ~15 samples (from one brand alone) and you can see that it may take some time to actually use up samples.
I do have some hoarding tendencies. I had the same thing with buying fragrance spray samples - biggest difference being that sitting in a 10ml spray decant for 2 years has not altered the smell; only a potential small loss from evaporation.