Help deciding if the bike is worth the money to buy

[Newbikeower]

Ok, I decided to buy a bike to get fit but not much of a shopper. There's a bike I seen that the owner has told me its a polygon siskiu 29er. I've taken it for a test ride and I love it. Easy smooth and comfortable ride but he is asking for $600 cause he has told me it has all the top of range parts. It has xc32 rockshox suspension, shimano deore hydraulic brakes entity elite trail frame with shimano 18 gears 2x9 speed and new maxxis tires. By looking online I can buy a cheaper MTb brand new.
Can anyone help me with advice on if this bike is worth $600 or should I buy a brand new bike that may not have the top of range parts?

[Calvin27]

Quite a stretch to say 'top of the line parts'. But if in decent condition, sounds like a decent deal.

By looking online I can buy a cheaper MTb brand new.

Not a dual suspension you're not.

[P!N20]

What are you planning to do with this bike? It's more suited to ripping along dirt tracks as opposed to riding around the neighbourhood to get fit.