Why do you keep denying that? Northerners were major slave traffickers. They bought and sold slaves as early as the 1630's
From the website theclio re Faneuil Hall - "The hall itself was built by artist John Smilbert and funded in part by profits made from the African slave trade. Construction started in 1740, and ended in 1742 when it first opened up to the public, and some of Boston's earliest slave auctions took place at Faneuil Hall. Yet aside from slave auctions and other public goods, Faneuil Hall was also the site of where Samuel Adams made an important speech as did several other patriots during the American Revolution, and in 1764 it was where Bostonians protested against the Sugar Act as they wanted no taxation without representation. "
Northerners find it very painful to learn that their ancestors not only owned slaves, but they made great fortunes in the slave trade. It was northern ships that carried many of the slaves and it was the north that rounded up Indians and sold them down in the islands in exchange for black slaves.
BTW - Clio is the Muse of History. The website is run and written by historians. They know more about the slave trade than public school teachers who perpetuate some of the myths about slavery.
I keep denying it because there has yet to be offered evidence. Some website opining that it happened means squat. Show me records of sales, inventories, certificates of title and I may believe your claim.