Is it Hard to Flip a Site that ONLY has Traffic Coming to it?

It wont be hard to flip no - the impact that website history has is the value; thus, the more history, the more uniques, the more you can generally charge !

However you can put it up for auction on flippa and eBay as an 'established business' ans see what kind of price responses you get...

It's easier than selling a site that has no traffic. The only problem is you can't show a prospective buyer the value of your site without a monetary income.

Find the right buyer though, explain that you haven't monetized it, but has a huge amount of potential with all of the traffic that is coming in.

I think that anybody new to this business would want to see how much a site could possibly make. Anybody who has owned a website or two will see any potential straight away.

Consider where to advertise your sites. Flippa might be fine but DP not, for example.

Since your traffic is organic, I would first attempt to monetize it before selling it personally.

Getting the traffic is half the battle to monetization.

I agree with "new" companies wanting to see income. But an experienced person/company knows a good thing when they see it even if it is not generating income. That can easily be amended with a redesign.

Before I start a personal project to flip I try and find my target (potential buyers) first with the intent of starting a bidding war for the site.
By using these potential buyers affiliate programs you are opening a door into their confidence if you do it correctly. Make yourself well known to the affiliate manager etc.. by keeping in constant contact with them making them feel as if you really value their input. This helps to gain favor.
You do this for all of your potential buyers.
Then start mentioning how you are thinking of selling the site (after you start getting the traffic). Once you get one offer tell all of their competitors. Many of these "big dogs" do not want their main competitors having something that they cannot have.
Then play them until you get the best offer. Most often when they buy the site from you they just dissolve it and keep the domain forever.
I can tell you that $20K+ is nothing to some of these companies. They spend that at lunch.

I prefer this method as opposed to creating hundreds of new sites just to auction off on Flippa. It takes more time but the rewards are higher. At least it seems to work well for me.

Good Luck!