Surprise pills can definitely be a surprise I guess.
Back when I was into that scene there were basic risk-reduction methods people would use to try to minimise the surprise.
Buy pure powders from sites that listed the IUPAC chemical names and structures of what they were selling. Even better if they listed results from GCMS assay on their supply. Make sure they could actually spell the name of the drugs they were selling. So look at listings for (e.g.) 4-MMC from a site the community trysted rather than a bag of "Plant food!" or "gogaine blend!" from a page that popped up yesterday and spelled 'methiopropamine' in three different ways.
Preferably get it tested yourself too. Basic mandelin, ehrlich, marquis chemical tests could give you some info on what you had but in the UK there was a service where you could send in anonymous samples for GCMS.
Always do an allergy test first, starting with a dilution of the substance down into the low micrograms.
It wouldn't protect you from an MPPP/MPTP type scenario, but nothing will (including buying mainstream drugs) and at least at that point you can be fairly confident of what you're taking. Depending how novel the substance is of course, you may not have the first clue as to what it'll do to you...
Wait for in vivo/in vitro test reports from others before consuming.
When it arrived we dissolved it in water at 1mg/mL so we could volumetrically measure 2mg doses accurately. Our first test doses were 500ug.
It took us so long to get though the jar that some mold started to grow on the solution, even though we kept it in the fridge! Not wanting to throw hundreds of doses down the drain we scooped off the mold, added Everclear (ethanol), redid our concentration math, and moved the jar to the freezer. Wild, innocent times.
Sadly, one of my friends in on the desoxypipradrol jar died from fentanyl contaminated dark web drugs a couple years ago.
> Our first test doses
implying there were more later
I'm genuinely ... horrified, impressed, and much more.
However at least in my circles nothing really bad ever happened
Was interesting to see that they weren’t entirely asleep at the switch.