Quality:
Multi-sourcing
Cannot be expected to provide improved quality on his own initiative. Will go by what all of his customers generally want. Also it is difficult to pinpoint the source of a defective part when are several suppliers.
Single source:
Supplier would be willing to provide specialized quality. Willing to improve quality as per the customer’s specific needs
more at http://www.citeman.com/4600-single-source-vs-multiple-sources.html#ixzz4DQgxyBF6