Growing, here is some food for thought you were talkin about the few yards that have some crabgrass established. If spreading weeds to other yards are a concern. Schedule your day as to do those yards last, mow around the small areas that have crabgrass, then just go back and weed eat the areas, rake up the seed heads you can and discard them. That way you could avoid acidentally spreading seeds. Don't forget to charge for the extra time it take and make sure to explain that once its gone you will do the same process when you start someone else's lawn to prevent as much as possible bringing seeds to their yard.