I am the one that got stuck installing accessories at dealerships when people bought stuff. They are very easy to install. I am sorta perfectionist so I always measured and used painters/masking tape to help make sure it was aligned perfect. I also used some prepsol or cleaner to remove all the grease and such before I stuck the sill protectors down. I never did a Tiguan; however, did many sportwagens and such. So I can't think of it being that much different to install one.
From looking at the ebay link. I would pull the protecting sticky cover stuff off the back side of the sticky tape closet to the interior of the vehicle first. Then align on the area carefully but making sure you dont press down hard yet. Once you got the alignment correct. I would then pull the cover off the side closest to the outside of the car. Make sure you created a little pull tab from this sticky protecting cover of the outside double-side sticky tape before doing this. At this point all the double side tape will be in contact with the surface and you can press down with some force to make sure it sticks/bonded well.
What part of SoCal do you live in?