$5K is a solid offer, not a lowball, but I would not sell this name for 5K if I owned it, and would not be in a hurry to liquidate it. A hot ongoing trend, not a flash in the pan. Getting hotter with time, not cooling down, IMO. Photobomb regged in at least 9 extensions (even .eu); all other versions regged too (photobombs/photobombing/photobombed/photobomber/s etc etc). I see you're on page 3 of google results for the term, even though you've just got a lander page for now.
Will only become more valuable. Right now I'd value in the 7 - 10K range. If you need the cash fast 5K is nothing to regret, but the name is worth more and if you can wait, or do some good negotiating, let that price hike up.
Did you send a counter offer?
If not, I'd personally recommend sending a 'sorry, not willing to sell at that price but thank you for the good offer' email. And see what comes back. Me, I'd hold out for a drop dead minimum selling point of 8K, and hold on to it for more if I wasn't in any hurry.
But that's just lil' ol' me
Welcome to Namepros.
Great name; when and how did you come by it?
Oh, forget making it a social media site, unless you have plans to social-media-ize photobomb photos. Let someone with deep pockets (I'm assuming you don't?) pay you a hefty fee for the domain and pay a hefty fee for developing it themselves.