throughout the years, i have registered close to 20 mopeds in AZ. because of the misinfo and disinfo i've received from people who are supposed to know better, i researched this myself.
there seems to be conflicting reports as to what is necessary to legally ride a moped in AZ. some people have been misinformed by both law enforcement agents as well as MVD agents as what is required. the statutes are written in a confusing, vague manner that could easily be misinterpreted, and not every public servant here knows how to effectively do their job and serve the public.
the moped wiki has the correct information, as well as links to the actual statutes.
regardless of what you are told by the cops or the MVD, this is the law. just because a cop says you don't need to have any paper with a moped (and many will), that does not mean that's the case. the same holds true for an MVD agent.
if you are confronted by any of these less-than-proficient public servants, and they are pushing this on you, ask to speak with a supervisor, and know the law (if it's a cop, answer no questions, but that's another topic which i will touch upon toward the end).
when registering a moped at MVD, if it has already been registered, and you have a notarized bill of sale from that owner, you are golden, as it will be on record. if you don't, you need to get one. you can basically have one of your friends do it if you buy a bike without one. as long as the bike has not been registered for 7 years, it should not show up in the system (though this number is not engraved in stone--i have seen them disappear sooner, as well as linger around longer).
as per the info in the wiki, if you have a bike that is off the books, you will need a level I inspection, which is free. once you get that, you can take that and your notarized bill of sale written by anyone, and get a plate--in theory, anyway.
this is where problems sometimes occur. some MVD agents don't know how to register mopeds. they will tell you that you need a title, or that you need to get a bond because you don't have the proper paper trail. this is all wrong. you have all the required paperwork already. that, your ID, and the proper amount of money should get you a plate.
if the agent requires you to jump though additional hoops, request a supervisor and stand your ground. if the supervisor is of no help, ask for that person's supervisor. i have had to do this on two occasions. had i not been a well-informed, albeit a raging fucking pain in the ass customer to the MVD, i would not have walked out with a plate.
remember, these are public servants. you are the public. i have always been polite in my delivery (no swearing, no personal insults), but very assertive and demanding of the service i pay taxes to receive.
as far as the police are concerned, several of them not only don't know the moped laws, but don't know how to even run them in their NCIC computers. i once helped a sergeant so he could do it, but i don't suggest that. it worked out fine in the end, got me on my way with no ticket, but i broke my own rule of NEVER TALK TO THE POLICE. it's their job to figure out how to do it. all i am required to do is provide my drivers license, proof of registration, and proof of insurance (AZ is a stop and identify state, so we are required to offer ID upon request from a law enforcement agent). if the officer starts telling you you can't ride the bike, he can't pull up the registration , or some other jackassery that doesn't seem like protocol, say nothing, and ask for his supervisor. record it if you can, and always be polite. (edited)