I am not sure how often that TSA opens bags to inspect contents. Years ago,they would leave a note that they had opened and inspected a bag, but, I haven't seen a note like that for a long time, since 2007 or so.
On this last trip, about 2 wks ago, however, I think that my bag was opened and inspected, because the straps were unvelcroed, and I always velcro them together to keep them out of the way. I had a small luggage scale in my bag that went missing, worth about $12-16, and I paid about $8.50 for it. It was more of a nuisance than anything that I didn't have my luggage scale when I got to Orlando. Couldn't check bag weights on the trip home before going to the airport. Just goes to show you never know what somebody is going to fancy.