It's pretty simple with LSD. You should buy it in blotter form. A piece of blotter can only contain so much of active material (fractions of a milligram). It's too small a dose for almost any psychoactive substances to have any effect on you. LSD and DOB are rare exceptions to this rule. So if you have something on a blotter, it's either LSD or DOB.
Now, DOB is very bitter, and LSD has no taste. If you put a piece of blotter in your mouth, and it tastes bitter, just spit it out -- that's probably DOB. Otherwise, it's LSD, and it's pure.
The times when you could be reasonably sure you are getting LSD if you are getting the drug on blotter, are long gone. There are many drugs that can be/are being distributed on blotter paper. Some of these have a very steep dose-response curve, and can be very dangerous in relatively minuscule amounts.
While it's perfectly safe (if a bit reckless) to consume, say, upwards of three hits of LSD on blotter, doing the same with blotters containing 25I-NBOMe or Bromo-Dragonfly could land you in hospital or even the mortuary.
Taking psychedelic drugs originating on the black market has, unfortunately, become an intricate game, and you really need to learn the rules before you can play it at least somewhat safely. There is no easy answer, other than doing your research, preferably lots of it.
The first part of your message is a rather dangerous misconception. Many, many drugs can and have been dispensed on blotter paper, often as LSD mimics. For dozens of examples, see DEA Microgram bulletins passim (http://www.justice.gov/dea/pr/micrograms.shtml).
The point about bitterness is absolutely correct though, and certainly any purported LSD blotter that tastes bitter should be suspect.
Interestingly, at least one non-psychedelic has been found distributed on blotter paper: alprazolam (See http://www.justice.gov/dea/pr/micrograms/2008/mg0508.pdf), for which I'd tentatively expect the bitterness rule also to work.
Those only test for the presence of any tryptamine, not LSD specifically. So even if it tests positive you could still be getting DOM/DOB/DOI. Which is bad, since those can kill you or else have serious negative effects if you take too much.
DOM, DOB and DOI are not tryptamines, but rather psychedelic amphetamines. This is an important distinction, as it means that the most common test kit (Ehrlich reagent), will not confuse them for LSD, contrary to what you said.
It is however true that there are substances which both fit on a blotter, and are indole psychedelics - e.g. 5-MeO-AMT, or other (other than LSD, that is) ergolines, such as LSB, ALD-52 (though these are extremely rare and (likely) share the safety profile of LSD). The Ehrlich test is not capable of distinguishing between different indoles, so you may get a case of mistaken identity in this scenario.
I'm having trouble finding in-depth information about what a Modified Ehrlich's Reagent LSD test actually tests for. Would you mind telling me where you learned they test for any tryptamine, and any more information you might have on the matter?
I believe Ehrlich's tests for indoles, a family which includes tryptamines, but also lots of other things. Colour tests are never conclusive; increasingly persuasive results are usually obtained by combining several different colour tests, for example this post discussing LSD testing: http://www.drugs-forum.com/forum/showpost.php?p=1101068&....
Both the blotter paper and the inks on it could have a taste. Also, the sensation of taste (or lack thereof) could be influenced psychosomatically, by conscious or subconscious expectations.
AIUI, the point is that a sane dose of LSD doesn't taste bitter, so if one rejects any bitter blotter then one would be erring on the side of caution - possibly rejecting perfectly good LSD due to a bitter ink or paper, but avoiding the great majority non-LSD psychedelics.
It's certainly preferable to identify a substance before tasting it, but it's not too late - spitting the paper out and rinsing the mouth out is likely at least to reduce the absorbed dose.
A perhaps more pressing problem is the risk of anxiety due to an innocently-bitter piece of blotter - I imagine a borderline-bad trip could be made much worse by a persistent fear that it would last >24h.
Of course, real caution would mean not eating anything cooked up by criminals in an illicit lab...
DOB blotter is sometimes a little thicker/larger since dosage is about 10x heavier than the equivalent of LSD. Bad mistake to make by the way since DOB is less tested, lasts considerably longer and takes around 2 hours to kick in.
I didn't know that LSD wasn't ever supposed to taste. Figured the bitterness was just from the ink on the blotter. Took three tabs, felt it a little (comparable to 100ug), figured it was just weak acid and so redosed five more tabs about two hours in. Even on heroic acid trips the longest I'd been away was eight hours. On DOB I stayed out for a solid 24.
Yeah, DOB (and any other DOx, I suppose?) seems pretty bad. Very bad trips are apparently both much more probable and much more unpleasant on DOB than on acid. I don't think I know anyone who tried DOB and would recommend it.
I spent a summer taking DOB once. I would certainly recommend it, in the right environment and once you know what you're taking.
However, this particular DOB was distributed in pill form, so people believed that it was ecstasy, so I saw a lot of bad things happen to people from it.
Its a really interesting psychedelic (in my opinion) but definitely needs to be handled with care. You need at least 48 hours after taking any appreciable dose to return to "normality" so if you are taking it, make sure that you have at least two days free.
Now, DOB is very bitter, and LSD has no taste. If you put a piece of blotter in your mouth, and it tastes bitter, just spit it out -- that's probably DOB. Otherwise, it's LSD, and it's pure.