Good Idea :thumbsup: Get in before the ban 'cause you know the restrictions are coming. Away from Cauliflowernia, for starters.
Most accommodating states for A 4 (AR 15) & "Ack four seven" -
If on the East coast, New Hampshire, Vermont (yes ! liberal socialist Vermont of all places !, the last time I checked anyway), Florida, an I'm certain the Carolinas.
As for the West coast, the most accommodating states - Nevada & Arizona, the latter, arguably the A4 • AR-15 center of the universe.
Get lots & lots of differing opinions and use your own good judgment or the judgment of someone you trust. Too many buyers have been burned - and I mean bad. Never buy anything used that you haven't fired at least 20 rounds through. If an individual is serious about selling his stick and he has nothing to conceal, in all likelihood, he'll give you a go at it at your local range, given that, you supply the major brand (Win. - Fed. etc.) name ammo to run through it.
Maybe this is a good place to start looking, at your local outdoor ranges. Phone ahead and see if there is a firearm sales & service facility, as part of, or independent of range facility. It's always best to have the proving ground right outside the doors of where your about to purchase a used firearm.
If you're just kinda getting started in this game, I would recommend that you buy a new unit. You can typically add accessories of custom cater to your particular desires later. That' the good thing about the '15, it's very modular. Learn all that you can before your purch. Unless you know a great deal about '47's I would discourage that you look at one. So many are built with a variety of parts from around the world - there's often out of spec issues etc. Good for a later purch in my opine.
Above all else Safety & Personal Responsibility First !
See ya out in there desert