Muddy Fox Pathfinder 90s MTB
We can't give valuations - that's considered off-topic because they're highly region-specific, and go out of date fast.
The bike you're looking at is available here-and-now, and the seller is asking a token sum.  In these days of C19 and shaky supply lines, any bike is better than no bike.
If you need a bicycle, and this one fits your body, you find it comfortable, and the bike is mechanically sound then grab it.

https://www.merriam-webster.com/dictionary/token%20payment says

Definition of token payment
: a very small payment made upon a debt and intended by the payer merely to acknowledge the existence of the obligation

If an item is given freely with no cost, then the receiver may not value it sufficiently.  By asking a nominal charge then the receiver is more likely to value the item, whatever it is.
I used to volunteer for a bike fixup, and there were a group of local kids.  Every 3 months they would come and ask for a replacement bike because they'd dropped their previous, or put it down and forgotten it, or left it outside and it was pinched.  A lack of cost and easy access to replacements meant they did not appreciate what they had.  
Problem was solved by asking them for the old bike back so it could be handed onto the next user.
So 10 UKP is there to make the buyer value the item, but seller also feels they've got something out of the trade.  The actual cost is small (often about the cost of one person's lunch, or sometimes as little as $1)