In the second edition of Mandl and Shaw QFT, on page 361, it's fairly obvious that there is a sign discrepancy between eqn (15.125) and eqn (15.127). In eqn (15.125), there are 5 imaginary i's and 4 explicit minus signs for a final product of +i. However, the first equal sign in eqn (15.129) gives eqn (15.127) an explicit minus sign, i.e. a final product of -i. Eqn (15.125) is created from fig (15.17b) and seems to be correct, but I am not completely sure. Can someone confirm that eqn (15.125) is an accurate application of the Feynman rules to Fig (15.17b)?