It won't tell you the percent of weed seed in it. The older the compost the more likely you won't get as many weeds.
It will show if you have high levels of metal (which you don't want).
Tell your customer you will get some weeds....but the one's I've gotten are in very large open compost areas, where any weed seed flying in the air could land. Once the weed seed hits the organic compost.....it's going to grow since its the best environment for grass and weeds to grow. We've walked up to these large areas and with a bucket.....just picked the weeds out....takes about 15 minutes. The weeds are far and few....but you will get a few.
In most yards....you are only fixing a few dead spots....so that's where the weeds will be. The rest of the yard so be weed free, since the lawn is already established thus keeping the weed seed from germinating due to the original grass/lawn.
Here's a PDF file of typical soil sample results that you can give to your customer....showing long story short.....that the organic compost is not going to harm their yard. Regular dirt is maybe one of the hardest things to get rid of.....since most places are worried about it's metal and toxic levels may hurt their yard.
2013 Ford F450 Super Duty Truck
2010 Exmark Lazer Z 60" deck
2012 ExMark 30" Riding Aerator
2011 John Deere Pro Gator 2020a
2011 Lawn Solution Dual Hyrdo Aerator 24"
2011 Echo Handheld (trimmers to power pruners)
2007 Big Tex 4ft metal high side 7' x 12' Trailer
2012 PJ 7' x 16' Dump Trailer
2014 Vintage 8.5' x 24' Enclosed Trailer
2012 Ecolawn Applicator model 200 Compost Spreader