Virtually all LSD that is sold is pure. The synthesis is well known and it's so cheap there is virtually no incentive for adulterants. Obviously some level of regulation would be better. But it is not at all difficult to acquire such a thing.
I don't know if it happens in the wild, but it is a possibility. By using more reagents, you may be more certain, but unless you take it to a lab with good enough equipment (such as GC/MS), you never know.
There are plenty of 4-aco synthetics out there though but those are all mostly very safe and are usually sold as mushroom/psilocybin equivalents not LSD.