Which is more important making the right item or finding a way to sell it?

Both are important but making the right item is by far more than half the battle. Selling something is an art form in of itself. Remember the pet rock? That was a advertising campaign that would make any company envious. More recent is the chia pet that shows up every time at Christmas. Both of them are novelty items that sold well because of their advertising campaigns. They were both very successful but how much did it cost for the advertising?

If you have a great but unique sewn article to begin with then you won't have to advertise it as hard as the pet rock. Put your effort into the item first and then into advertising. The item will sell itself to your customer - if it is a good design and very well made.