Those who recommend "chemical overhauls", do you really want that gunk that is in that carburetor dissolved and run through your engine(s)?
Based on personal experience as an Outdoor Power Equipment mechanic, having worked on units that such chemicals were used in, I say "Not me!"
Every year, we got units in the shop that the owners had used just about any chemical you want to name (Seafoam, home-brewed Seafoam, Heet, Iso-Heet, Gumout, acetone, Sta-Bil, etc.). In the end, most of them had to bring it to the shop and have the carb rebuilt or replaced (some of the harsher stuff actually damaged parts of the carb!)
OP, go ahead and buy the generators, then take them to a reputable shop and get the carbs cleaned properly, the oil changed, new filters and spark plugs, and the generator output tested and set for voltage and hertz. Use your favorite fuel stabilizer in every can of gas right from the start, and you should have no further trouble.
Good luck.
CM1, USN (RET)
2017 Jayco TT
Daily Driver: '14 Subaru Outback
1998 Dodge QC LWB, Cummins, 5 speed, 4X2
2 Kawasaki Brute Force 750 ATVs.
Pride Raptor 3 wheeled off-road capable mobility scooter
"When seconds count, help is only minutes away!"