This is called "Dual Agency", and it is not at all uncommon. It must be
disclosed by the agent, and there are some very specific rules (which
vary state to state) about what they are and are not allowed to do.

Have they actually retained this agent as their buyer's agent, or is it
just someone they stopped in to look at houses from? These are two
completely different situations. If he/she is not your friends' buyer's
agent, there is no fiduciary duty, and he/she works completely for the
seller. Again, not at all uncommon, just realize who's interests are
being represented. If this is the case, they may want to retain a
separate buyer's agent to represent them (or at least a lawyer to look
over paperwork; an agent can help with valuations and suggestions too).