Dangers of buying a used iMAC

While plausible there currently aren't any known scams of stealth software being intentionally left on a used mac, but a drive reformat and clean reinstall is the official recommendation all the same when transferring ownership. What to do before you sell or give away your Mac - Apple Support

The only real risk I know of for purchasing from an individual is that if Find My Mac is ever enabled and the mac is remotely locked from an iCloud account you can't access then Apple requires proof of purchase from an Authorized Apple Reseller before they will help you unlock it.

Also Installation DVDs were only included with macs that originally shipped with Snow Leopard or older. If the mac originally shipped with Lion or later then the seller will not have an installation DVD to pass along and a clean system reinstall will need to be done via internet recovery.

John,

If you are considering buying a used Mac, my recommendation is to purchase from a reputable source such as www.macsales.com. If you buy from a private party you never know what you are getting, if you are worried about what is installed then ask for the original install discs, if the seller cannot produce them then pass! You can always wipe the system totally clean and re-install Mac OS if you have these DVDs. Then you can upgrade to a much more current version of Mac OS.

As stated, you can simply wipe the drive clean and start over.

Something to consider, repairability. iMacs are very difficult to repair.

With a 5-6 year old hard drive, it may be living on borrowed time.

In addition, spending only a few minutes checking something out,

may not expose issues that can crop up after running for several

hours, i.e. heat related.

I agree with rkaufman87 that a computer such as an iMac should

be purchased from a reputable source. In the case of Macsales,

they have a 14 day no questions asked return policy and a 90 day

parts and labor coverage should anything fail. It will cost a bit

more, but it has been inspected and fully tested for defects.

I agree with others posting here that a iMac should

be purchased from a reputable source.

Might be better to pay a little more and buy a certified refurbished iMac from apple than to deal with an 5 or 6 year old used hard drive.