I look at FB marketplace, Craigslist, Ebay, Pink Bike Buy&Sell to get an idea of what people are asking for the same or similar bikes. searching EBay ‘completed listings’ can be more beneficial since it shows bikes that are actually selling as some of the other sites have people who overprice their bikes and they sit on there unsold forever.
I take all that info and then price it a under what else is out there so it sells more quickly. I’d rather get things done quickly and make a little bit less than have it sit for a while and keep answering messages asking things like “is it still available?”
The other option is to fill out the form for Pros Closet. It’s the easiest way to do it. But the downside is you would likely make $1000+ less selling to them than you could doing it on your own (at least this was my experience when I looked at selling a bike to them last summer)