How to unlock an icloud activation lock?

I bought an iPhone 8 Plus off of someone on Craigslist and it turns out the device is icloud locked. I spent a lot of money on this phone already so I would like an inexpensive, free way to unlock.

It might be stolen, contact apple and depending on what they can clarify, the police.

You are a victim of a scammer using Craigslist.

You have become the second victim then, as the first is whoever that phone was stolen from.

The phone is permanently useless to you. There's no way to defeat Activation Lock unless you are the legitimate owner.

Your money is gone and the stolen phone does not belong to you. The best thing you can do with it is to hand it in to police so that there's a chance it might get back to the owner.

People who buy used phones without checking them properly before handing over their cash are exactly what still drives thefts (often violent) of mobile phones.

Your best hope now is that there's a small reward for the safe return of the phone.

Keep hold of it and the phone might be tracked to where you are, using either Find My iPhone or one of a number of optional covert tracking apps which also take secret photos on both the front and rear cameras which get sent to the owner/police along with the time, date and GPS location of each image.

There's no way. Its a security feature not meant to be bypassed. Unfortunately people take advantage of that & sell (knowingly) iCloud locked devices.