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In my limited experience, landing pages for each service and/or "service in city" work nicely as a part of a content marketing strategy along with blogging, etc.

It is Bing that says it is incorrect, not me. "To be clear, using the rel=canonical doesn’t really hurt you.  But, it doesn’t help us trust the signal when you use it incorrectly across thousands of pages, yet correctly across a few others on your website." You are correct in that it does say, "no need for that" and says the use is incorect. So why do it?

In the title tag, just use & (with spacing). Not & - see AT&T website.

Thanks Adam, that would be very awesome of you and your team!