People want a great offer today,....not in a month or two, and after finally finding a great customer, you then have to do a free mow?
Better off doing the opposite and use it to quickly weed out customers who you don't want.
eg: instead of offering a percentage off, make an offer of x$$$$$ off your first mow!
Make it clear that it a one off per customer. Make an offer that at least covers your expenses minus labour,but seems too good to refuse,.... and I will guarantee that you will build a client base very fast.
Once you have your foot in the door, have done a good job first time, ....they will accept your full price quote, almost whatever you ask.
The main thing people decide on when choosing somebody, is how much they like you as a person, followed by your work standard, and lastly price.