The main theorem here is the K-theoretic analogue of the cohomological `stable double component formula' for quiver polynomials in [Knutson-Miller-Shimozono 2003]. This K-theoretic version is still in terms of lacing diagrams, but nonminimal diagrams contribute terms of higher degree. The motivating consequence is a conjecture of Anders Buch on the sign-alternation of the coefficients appearing in his expansion of quiver K-polynomials in terms of stable Grothendieck polynomials [Duke Math. J., 2002]. (Simultaneously and independently, Buch has obtained a different proof of his conjecture.)