If you have an off season send them a quote for next year with an increased price and require a deposit for the first service. Let them know that a credit card must be on file for automatic processing for the season, if the credit card does not process take them off the schedule. A lot of landscaping companies are moving to pre-paid monthly services, it may be in your best interest to enforce it with those particular customers, if they aren't in agreement they will cancel on their own.
Thank you - I like this idea but it won't work for a lot of our older clients who prefer to pay by check or cash. But those clients are never the problem honestly.
