Unfortunately, the used market is a total mess right now. I was looking for a spare recently and honestly, the prices are sticking way higher than they should be for a camera that came out years ago. Ebay is particularly bad... half the listings are overpriced or the bodies have like 100k shutter clicks, which is just not worth it imo. If you really want to stay under that $1200 cap and not get ripped off, you gotta skip the big auctions and try these specific gear sites:

• MPB Used Sony Alpha a7 III Mirrorless Camera - they actually photograph the specific unit you are buying, so you can see if the sensor is clean or if the rubber is peeling.
• KEH Camera Sony Alpha a7 III Mirrorless Digital Camera Body - their grading is super conservative, so an Excellent usually looks brand new.
• B&H Used section - sometimes you can snag an 8+ or 9 rated unit right at your budget. Just a heads up, if you cant find an a7iii at the right price, you might look at the Sony Alpha 7C Mirrorless Digital Camera. It has the same sensor but the autofocus is actually a bit stickier for tracking subjects. I had some issues with the smaller viewfinder on it, but for a trip to Japan, the compact size is a huge plus. Definitely beats lugging a heavy kit through Shibuya.

Omg you are going to love Japan! I took my Sony Alpha a7 III Mirrorless Camera Body to Tokyo and Kyoto last fall and the shots I got were just incredible. Honestly the low light performance in those narrow neon alleys is amazing! About the price though... I was in your exact same shoes last year trying to squeeze every penny. I ended up trying Greentoe because I was super skeptical but it actually worked out fantastic. I put in an offer for $1150 and it got accepted within like four hours by an authorized dealer. It felt like a total steal since it was brand new with the full warranty! If you are really pushing that $1200 limit you should definitely check out the used section on B&H Photo too. I found a Grade 9 Sony Alpha a7 III Mirrorless Camera Body for my brother there and it looked like nobody had ever even touched it. eBay is honestly a mess right now with people overcharging for high shutter counts, so I would stay away from there if you can. Ngl Greentoe is the secret weapon for getting that brand new gear feeling without the retail sting. Just make sure you account for tax in your offer because that caught me off guard the first time. Have the best time in Japan, its literally a photographers playground!

I spent ages deal hunting before my last trip and it's definitely a lot to manage. Are you looking for brand new with a warranty, or would open-box work?