Is the powder less potent/cut? Otherwise, I wouldn't see the point in buying the paste, since after drying the paste, you end up with less weight, extra work, and less bang for your buck. Talking about high level vendors here too, with tons of feedback.
Usually you use weight with paste, 25%-45%. So if the vendor sells 5 gram paste for the same price as 5 gram powder, he either cut his powder, or really bad in marketing/math