They are highly trained animals who use a system of behavior and reward. Because of this, it is fundamentally important that all of the attention received by a guide dog come exclusively from his or her handler. Folks will have to resist the urge to pet, talk to, make cute faces at, make eye contact with, or call by name a working dog. This kind of inappropriate attention confuses the clarity of the dog's training and interferes with the safety of the dog and it's handler. If there is ever any confusion about this, it is always okay to ask the dog's handler any questions you may have.
Guide dogs do get to play, but it is exclusively with their handlers.
This side of the working relationship is often not visible to the general public. It is important to realize that no dog graduates as a guide who doesn't really love being a working dog. Part of the communication between the handler and dog comes in the form of leash signals. This does not hurt the dog in any way. A dog's neck is the strongest part of its body, much like a person's thigh.