I thru-hiked in 2009 at age 50. I had never hitch-hiked in my life so had the same worries before my hike. As it turned out, I never had a problem hitch-hiking. When you are trying to get to town from a trail-head, it is not like what I imagine hitch-hiking is like elsewhere. People know you are a hiker, and lots of them pick you up just for that reason, even though they wouldn't normally pick up a hitch-hiker.
Whenever I hitched and had to put my pack and poles in the back of somebody's truck, I always worried they would inadvertently drive off before I got my stuff out. To protect against this, when I got out of the truck cab I would leave the passenger door open, go back and get my gear out of the back, then walk up, stick my head in the door and thank the driver again before shutting the door.