looks older than "6 or 8 years". more like 68 years old. Seriously though, check the date code on the engine, I bet it's closer to 20 years. Maybe more.
450 sounds like alot. Have you priced new ones just to get an idea of a used ones worth?

Judging from tine / tire wear and it's overall appearance , it has seen lots of use. $250 would be more realistic. $150 would be better.

Its a PTO Horse model, newer than 1985, the cross rib pattern on the side of the tine shield tells me that its newer than mine. Mine is a Horse III, year 1985. From the first picture I'm trying to tell if it has a clutch disengage lever under each end of the handle bars. Sort of a deadman safety feature. This was called OPC- "operator presence control". If it has this feature I would say you have a OPC PTO Horse 4. REJ2.

This looks like a "real" Troy Bilt Horse made by Garden Way Mfg before they threw in the towel.

I don't see the Hi/Lo lever and it looks like the T shaped handlebar pivot handle busted off.

I'd guess this thing is from the early to mid 90's. It was one of the last Horse models since it has the 8 HP Kohler.

It looks like it's in fair condition and certainly not a cream puff. Look it over very closely and check for damage and/or abuse. Make sure the tranny seals aren't leaking. Tines can be replaced but major parts and casting are getting scarce.

I wouldn't be too excited over $450 but he might get his price if he waits until Spring since these old Troys are so sought after. I pretty much agree with the other poster that $250 would be a good buy if it's actually in better shape then it looks.

If that Kohler Mag. and it's in good condition it's worth 300. along. Have you priced Kohler Mag.?? At least 700 bucks) the cast iron frame and gearing looks like surface rust to me from put away wet and dirty. A good cleaning up and some paint and you're got a 1000 dollar tiller providing you tested it with no problems. Money well spent IMO when compared to the 500 to 650 MTD tillers

I would have to agree with Davefr's comment. "Tines can be replaced but major parts and casting are getting scarce."

I have an older Tory Mini Tiller. I can't find replacement tines. Discontinued and sold out. My only chance to find tines is at yard sale and a lot of luck. Make sure you could buy parts before purchasing. Hope this helps.

It looks like it spent its entire life outside with a tub over the engine.

On top of what's already been suggested -

Look at the tires real close. They don't look too bad in the pic, but rubber and sun do not get along at all and they could be shot. A new set of tires mounted will cost between $50 and $100.

Maybe I don't have enough knowledge to say this, but the tines look OK to me. If you're doing and 30X50 garden with this, they'll last years. Otherwise, a quick check on ebay yielded a seller who sells tines that he/she claims fit all years of the horse tiller for $100.

Check the oil. If it's black sludge, it has never been changed. If it's brand new, they could have just changed the black sludge, but if they didn't care to change it all these years, they probably didn't think if it now.

The biggest thing I'd be scared of is the fact that it spent its entire life outside. A tub over the engine is NOTHING compared to a garage. Moisture has a way of getting everywhere you don't want it. I'd pull every plug on this thing and check what the fluids look like. I'm not familiar with this specific model(I have a couple BCS tillers), but there has to be some sort of gearbox for the transmission and one for the tiller. They could be chock full of water - bad, Bad, BAD.

When haggling, mention $100 for new tines, $75 for new tires, and at least $20 for various engine and gear oil changes. Bring up concern for the fact that it's been outside for 15 years, twice. That should get him to a more reasonable price.

I don't believe parts are at all hard to find for the horse model. Some online parts suppliers have a dedicated Troy Bilt tiller section. Bearings, shafts, gears, seals, shims, all easily available if you take the time to look. Individual engine parts are also out there, but replacing engine sometimes is more cost effective. Go to the online auction place, "e-something", check various spellings such as troy bilt, troy built, ect. You'll be supprised as to all the parts listed. Check vendors at the bottom of the page, castings, transmissions, tines, its there at times. Granted your not going to go to the average small engine shop and find what you need but it is out there. The guy that runs the troy bilt tiller club claims he has every part for any 1970 and up horse tiller excluding engine parts. He formed the site for the sole purpose of exchanging info and keeping these wonderful machines running. REJ2.