Seeing that the 1200 has a composite monitor output, the seller could have hooked the computer up to a TV to see if it booted to a Workbench screen. Could be one of those sellers who found the machine laying around and is just trying to make a quick buck off of it based on past auction values. My reasoning for bypassing a stock 500/1200 and going for a "big box" machine was the same as yours. Once I found the needed RAM and storage upgrades, the cost becomes a wash.
The 2000/2500 and 3000 machines are reliable enough that unless they have battery corrosion, most "untested as-is" units on ebay can easily be brought back into service. Unless you have a stockpile of ZIP style memory for a 3000, the 2000s will generally be cheaper to upgrade memory on. Also when buying an Amiga, ALWAYS get a photo of the battery area of the motherboard. The only exception to this rule is the 500 (but not the 500+), 600, and 1200 as they didn't come stock with a RTC.
Hang around Amibay and browse the listings and post a wanted request in the appropriate forum. Eventually the machine you want will pop up here in the US. Shipping from Europe is cost prohibitive at this point, plus the machines come with 240VAC power supplies which have to be swapped out for 120VAC units.... which adds to the price.