The quickest way to weed out almost all scam emails/texts regarding craigslist items is the scam emails almost never mention the item details directly because they cut and paste the text to so many responses. It is always "Do you still have the item?" "I really like your listing" or "I would like to buy your item". Where as a real interested person will usually assume the seller may have more than one item for sale and will mention it directly "I am interested in your pioneer trailer" or "I am interested in your Yamaha motorcycle, do you still have it?"
Regarding the phone scams, the IRS will NEVER call you over a legal matter, they will always correspond by mail or certified mail. I did have one that gave me pause, I got a call from "detective so and so from the Los Angeles county sheriff department regarding a credit issue that could cause a warrant to be issued and I needed to call right away" This was very good because where I live the LASD has jurisdiction, the caller had no accent, and the SD certainly might call if they were investigating something. I googled the phone number and found it associated with a scam, but it was one of the better phishing calls I have gotten.