For me (and other sources), it is. My merit page reads
"You are a merit source. The next XXX merit you spend will come from your source rather than your sMerit balance. Merit spent from your source will come back in 30 days. Unused source merit is wasted. It is not allowed for merit sources to sell their merit."
As sources are the only permanent holder of sMerit (they regain their limit every 30 days), this generally disallows the sale of Merit on a long term perspective.