He lied and caused you stress, delay in the sale of your house, and some safety factors. He should be reported with as little cost to you. He has probably operated like this before and it won't be his last.
Does every wholesaler behave like this? Is what "they" do illegal? The answer to these questions is NO! Don't believe the brokers and agents and haters who say so. There are legal ways that a wholesaler can operate, in an ethical fashion, and still complete a win-win-win-transaction. I believe they are few and far between.
You, as the seller, should have asked him what the "assignment: means, if you didn't understand it. Lesson learned. He said he was a cash buyer. No need for assignment clause.
Should that put a bad taste in your mouth towards all wholesalers? I think it should arm you with what to spot as legit and falsehood. Maybe next time faced with someone exhibiting the same behaviors or signs gives you great power to call them on it. Lots of great advice on how to prevent most shady wholesalers (and other unscrupulous cash buyers) from the get go. Ask for EMD and ask for Proof of funds. Even then, I've seen some real good bogus letters with all the official, trademarked and copy-written logos and what-not and wasn't worth the paper it was printed on.
Even so, There are some legit deals that are being made everyday between a wholesaler and a seller where both are happy with the result. Now, whether or not they buy it or have a cash buyer buy it makes no difference as the desired result was achieved. If it doesn't sell, that could be due to a number of reasons. None of which matters to a seller. They just want it sold for the agreed price and the agreed time.
I, as an aspiring wholesaler, will operate legally, ethically, honestly, and be as transparent about how I operate to both the seller and the buyer. However, before I start business, there are some things I'm doing to make sure I for one, can do what I say (If I state I will buy the house, I better damn well have the means to do that). Have a team of professionals, an avenue for funding, a list of buyers that I know are looking for certain properties (even if I don't, if the deal screams "good deal" that should entice the buyers to step up), etc. I'm "investing" a decent chunk of money up-front to be the best wholesaler I can be.
Actually, seeing it from the buyer side (fix and flip), I had very limited true deals when receiving from wholesalers, which is what gave the bright idea to be a wholesaler myself. If I can find and negotiate the deals I want, that's better for me and cuts out the middle man. If I come across and actually negotiate on deals that are still good, but I don't want to buy them (like a full rehab or just a particular market or area or just doesn't fit my criteria), then I will pass them along to other investors. I may even assign a few if there is some money I can take off the top. Is there anything wrong with this?