Many sales people assume one way to immediately show a customer connection is to use their logo in a proposal document - either on the cover or throughout in the header/footer. The idea is probably to subliminally convey a partnering spirit by associating your brands together. This is a bad idea. Logos are important assets of a company, they are core elements of a brand identity and treated with respect by their owner. Companies will carefully define their own logo usage in identity guidelines. Why then would they feel good about another business, trying to start a relationship with them, taking their logo (probably in a low-res format from the web) and sticking it on a proposal back to them? Best intentions here are likely to backfire and create the opposite reaction because it is actually disrespectful, apart from abuse of copyright. Not a good way to start.