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The man says it holds air and it's the rear. It's a plus wheel going to be used rarely for beach trips , rocky places and will never leave the ground.
Safe or not?

If it was on a bike I already owned I'd live with it until it failed. If it was a new (to me) bike I'd be knocking off the price of a new wheel..
Best thing you can do is put 30 psi in the tyre then put some soapy water around the damage if you get bubbles he's telling Porky's , no bubbles no leak, and it will suit your purpose.
If it was on a bike I already owned I’d live with it until it failed. If it was a new (to me) bike I’d be knocking off the price of a new wheel..
Or at least a new, identical, rim.
I think we’ve all had wheels hold air in much worse condition.
As Volksman says though, put a lot of air in and see if any is seeping out.
I’d buy it, but it all depends in the price.
From a safety point of view, impossible to say, but I’ve had wheels an awful lot worse than that and they held up fine, for years more abuse.
I've got worse on the front of a 22kg ebike, did it on its first ride, I'll ride it til it dies.
As SR says, worst case scenario you change the rim.
If it were me.... walk away.
It's got an hd driver so game over.
Looks alright to me, but I'd want the price to reflect it. Swapping rims is pretty straightforward even if you've never done it
If it was already mine I'd carry on riding it but I wouldn't be buying it, or at least getting g the price of a new rim knocked off.
The ding is rather nasty but what interests me more is there seems to be a stress line in the stickers at each of those spokes.
I would ride it most probably on the rear might last long time but would consider it more likely not too. would not spend more then hub value on it.
Done similar ding to my rear on one of its first rides going through a rock garden on slow puncture.
I think those "stress lines" are just reflections of the spokes
Not unusual to see dented raceface arc rims. Looks worse as the decal has cracked but I can't zoom in to see that else is happening along the bend line so I might be missing something.
Assuming the metal under the decal isn't split or passed it's deformation limit then I'd be at that with a crescent wrench to straighten it out but it's probably got a bit of a flat spot too. Arc rims can be had pretty cheap (well, could be pre COVID)
I'd ride it no worries, but the price would need to be a bit less than an otherwise identical bike with a straight rim.
I dinged an old Crossmax SLR a lot worse than that, pulled it back into roughly the right shape and got another few thousand miles out of it before selling the bike.
As above, as long as it holds air I wouldn’t be too worried. Even if it doesn’t hold air it looks like it can be fixed. As long as the rest of the bike is good, what you’re after, and reasonably priced, I’d say go for it.
I would want to see it in person, also to check the spoke tension.
I'm just buying the wheels. Want some plus ones for my whippet.
I would avoid unless they are super cheap and you can factor in a new rim / rebuild as I’d say it will need it at some point.
These are top of the pops now. Probably not that good but might only get used twice a year and means I can sell my fatty.
https://alpkit.com/products/sonder-nova-27-5-wheelset
apart from what looks like a crack and the ding they are fine. especially as it won't be me riding it 😉