You might ask the guy if he used stabilizer or not. Seems to me he may have due to knowing he wasn't riding it much and the nature of his bees nest. (a double dose of stabilizer last for two years.)
If the sickle is local, go over (+1 greybeard) and put about 4ccs of oil in each cylinder, drain the carb bowls and let some tank fuel pass through to observe both the colour, smell and trash/water if any appears in the collection vassal. Take the battery out and bring it home to charge it up.
Now, based on what the gas looks like, go back the next day with some gas and spark plugs, then either drain all the fuel or not. Look for a nest in the airbox. Hook up the charged batry and see if she'll start.
If you decide to purchase expect to spend round abouts of $450 bucks to correct any
problems. New skins $300 + oil change out $50 + rear brake pads $30 + sundry $70.
Sundry: NGK DPR8EA-9 spark plugs, brake fluid, wax, condoms, beer.
Alternatively, in a 'either or' scenario, go over with a hot batry and a clean supply of gas, drain each bowl, decide whether gas is bad or not, take a gander at the air cleaner, then try to fire her up. You are relying on his representations.
Bring a tire pressure gauge with you as well.
Good luck! Sounds like a sound deal to me.