This may seem obvious - but yes, consult others before using them as a reference. At a minimum, you'll want to know they're happy to give you a good reference.

This may seem obvious - but yes, consult others before using them as a reference. At a minimum, you'll want to know they're happy to give you a good reference. One would hope you've developed a strong enough relationship with some colleagues as humans (i.e. beyond the confines of the "employee" relationship.) Humans don't always stay at one company forever. Trust comes first - the rest follows rather easily.