(Folks: dwestcotttt03 and I have already talked by email directly, but I'm also replying here, in case it's helpful to anyone else down the road, purchasing a used Harbor Freight greenhouse.)

I haven't disassembled one yet, so I was hoping we might get somebody with more transport experience to post here. I'm really not sure if you'll be able to completely avoid dismantling the walls or not; my approach would be to remove the panels, and then "feel my way" through the dismantling process, to see what's possible.

A few "heads up" comments:
You might be surprised that the aluminum in these kits is softer (easier to bend) than some aluminum. For example, the aluminum stock sold at the box stores is harder than the kit material. So, I think the larger the pieces you try to move intact, the easier it might be to accidentally bend some of the components. Just mentioning this so you can watch for it, if trying to move large sections.

I'd remove the polycarbonate panels to avoid damage. Since the greenhouse is used, it may have been exposed to enough sun (depending on the age and shadecloth use) for the panels to have lost some of their original flexibility. Over time, my panels have become more yellowed and brittle, requiring eventual replacement, and they are easier to crack or break when they become a little brittle.

Hopefully the previous owners have not caulked the panels in place. (I have not, but some folks do, to secure the panels.) If they are just secured with the Harbor Freight spring clips, you can pop the clips out out of the track by sticking a screwdriver under either the top or bottom “foot” of the clip, to pry it out of the track, and then the clip usually falls right out.

If the previous owner has screwed the panels into the aluminum frame (which I highly recommend, when you reassemble) then I’d mark each panel with a black Sharpie pen, and number them, so you can put them back in the same position. This will save you having to redrill the holes to reattach the panel screws, without having to play musical chairs later, to see what panel goes where. I unscrew and screw my own panels all the time, using the same screw hole in the framework, no problem.

Harbor Freight parts come with little sticky paper round labels, with parts numbers. Many folks just leave them on, which would be a help to you. If not, you could number the aluminum parts with a Sharpie marker, to make some kind of reference (roof, door, back brace, etc.) Or, if you are methodical, you could number them by using the part numbers shown in the Harbor Freight manual. That would probably be my approach, if I was brand new to the Harbor Freight greenhouse. (Then again, I’m rather a hopeless detail wacko.) A bit of lacquer thinner would remove any of your marks on the aluminum later.

If the previous owners did not keep the manual, you can download a 10x12 manual from the Harbor Freight website. Harbor Freight has revised the manual several times. A kind HFGH owner has just alerted me today that the newest manual, shipping with new kits, is different from the downloadable PDF manual on the Harbor Freight website. Apparently Harbor Freight hasn't updated their website yet, and the newest kits even have some new parts that the old kits didn't have. However, I'm guessing the current PDF manual should work for you, since your greenhouse is used, and any changes are hopefully pretty minimal.

Keep track of all the bolts. They are perhaps a tad soft (not the greatest quality) but the heads are specially shaped to slide in a grove in the wall and roof studs. It’s a little hard to buy regular bolts that will fit in the channel as well as these, if you lose or damage them. You can probably order them from Harbor Freight, but I don’t know how quickly they ship these.

And, as we discussed, photos before or during the dis-assembly process are a great idea.

Congratulations on the good price!