You're responsible.
If jonny buys an apple from sara and sara dropships the apple from peter, and the apple is delivered sour, jonny can sue sara if she doesn't rectify the situation. Sara would then have to sue Peter.
If justin borrows $10.50 from jospeph, and justin lends his only $15.00 to steve, when joseph wants his money back from justin, justin cannot tell him to get it from steve, unless joseph is willing to go through the hassle.
Unless of course an written agreement is made explaining these details