Been ramped several times.
How they act depends on many, many things. First, why are they out there? Is it political? Are they receiving pressure to "bust" someone? Has your airline recently been in the news? If so, watch yourself!
Most of the time it is routine, just filling a monthly quota. Sometimes it can be a surprise and startling.
I was on one of my very first charter flights, about a week after my checkride back in 1992. I dropped my passengers off at Merrit Island and a fed walks up to the Shrike Commander and says, "Excuse me, is this a charter?" He was obvioulsy expecting me to say no. I said, "Yes it is." He says, "Oh? I don't recall any Shrike Commanders on 135 in our district. Let me see your manuals."
He wasn't satisfied until he found our Ops Specs that showed this particular airplane on the certificate. Then he was very congenial. Good thing, too, because I was so flustered I started the left engine, only to have him wave at me and point at my back door (it was still open!)
In all cases, however, the ASIs (Aviation Safety Inspectors) have been polite and professional.