Originally Posted by Bowgie

I've bought airlines and hotel miles before with the respective program affinity credit card. I expected to get double miles or bonus points. In each case, the points sale was actually processed by Points.com, which meant only 1x miles

Not sure about United specifically. Read the fine print. If the sales is processed by Points.com even thru a link from United.com, then one gets only 1x miles or points no matter what card is used.