I don't think we can afford betting turn with this hand in a multiway pot.
And river as well. Do you think BTN will call with worse?
As far as hero calling goes. If BTN even considers having bluffs we are blocking a decent amount in 98s and some spades. We do block one combo of 87s. Does not feel like a call. But your mistake is on earlier moments.

Your bluff catching too wide if you call with 88s here, esp multiway

I agree with first comment, you should check on the turn.
There is not much raise for bluff on the river in NL5.

I think the very small turn bet is fine since SB min donk the flop probably with a veryyy wide range and BN can also call with close to 100% of is pf range tho. You still beat all the 7x and 5x. BN could have easily raise a strong T on the flop like ATs, KTs, maybe QTs.

I would check (and probably check-call) this bad river for our range here almost everytime to give BN an opportunity to bluff all his floats.

As played, fold to the river raise for the reasons said above.

With the turn bet you are building the pot up, for no reason with a mediocre hand in my oppinion.
If you want to fold AK or some wired hand you think he called the floap with , than bet 25% to 33% of pot. But you said you have no info on the guy , 66 hands is nothing. Sure , once in a blue moon he may show up, if you call the river, with 8-9... but the rest of the time you lose. Just give it up , it`s fine.
Do not hero call that :) .