The unevenness of the tone appears to be a result of whatever was applied to the blotter being repelled by the graphite. This suggests to me that whatever the brown substance is, it was applied AFTER the pencil. This sends up a red flag in my mind, since sheets are generally dipped without markings, both because graphite would make the distribution uneven, and to avoid detection during transport.
It could be that something was spilled on the sheet after it was marked, which is careless and could possibly damage the LSD, depending on what was spilled, and could have also resulted in loss of potency if the careless person in question attempted to blot up with spilled substance. It also could be the case that these tabs were manufactured by an amateur, possibly using an impure or low quality product, which you have no way of knowing is in fact real LSD.
It is shitty of them to try to pass this off to you, especially since you seem to be a good customer, and are making a substantial purchase. Get in touch with your dealer and ask him what is up. If he has anything clean that you can exchange it for, then do that. Otherwise, get your money back. If he won't let you return it for your money, then he obviously lost a good customer. I wouldn't put something that looked like that in my body, personally.
Note: if my theory holds water, then the darker lines were applied after the lighter lines, since the brown substance is pulling away from those lines as well. It is hard to say if the dark lines were applied before or after the brown substance. In any case, I wouldn't worry about the dose being divided up the way it is. He may have been planning on cutting it into 2-strips either for sale (perhaps pushing 6 for the price of 5 or 4 because no one wants that shady looking shit) or personal use prior to your contacting him.