You see them priced both ways for early guns. It is a selling feature not a deal breaker to me and dealers will try to pay less for which ever one you have. I had early double trigger gun, a well known dealer told me that everyone wanted single triggers and he reduced what he would allow me for mine because it had two triggers. At the same time another dealer had a two trigger gun for sale at a premium price because it was rare to see one with two triggers. Buy low, sell high, dazzle them with BS. I found the early guns to be just very basic guns while the later ones did have a lot more modern appeal.
Buy the gun and condition not the number of triggers as a rule. There are some buyers who will gladly buy a two trigger gun, a few who care not one bit either way and some who only know how to shoot single triggers. When it comes time to sell you may find a little resistence because of the extra trigger or you might sell it faster
