Been doing this type of work for 20 plus years. I have from the get go. Been given a bottle of booze or $20.00 gift certificate. This could be for car washes or good for gas. One year, I gave hams near Christmas. Trust me, This goes a long way. Even better then a Thank You. This will also show you, yourself how much you are appreciated for your business and the work you do.
This is done to the top 20 accounts , No signed contracts and I'm not looking for work.
Give, and you most likely will receive. Try it, You might like it.