The worst case scenario is that you don't get grass now or in 2-4 weeks. The seed will be "dead" in the sense that it won't germinate once it has come in contact with the chemical. I think it is less likely that you get growth and then the young grass dies as the roots go deeper, more likely is you won't get growth at all or significantly less than you had planned for (say 1/4 or 1/3 germination rate, btw totally just throwing a random number out since I have no idea if anyone could give a good estimation). You can keep trying every couple of weeks and not need to rake up the "dead" seed so no worry of overseeding as if grass does take it will eventually get the nutrients from the decomposing seed and will also supply a bit of water retention properties when watered. If you are going this rate and plan to seed after putting down soil I would make sure the chance for germination is highest. That means eliminating the air barrier when seeding and applying a light coating of soil on top of the seeds. For large plots of land the easiest way is to seed, top dress by hand or tractor/mower 1/8-1/4" with soil, apply a starter fertilzer (the grass seed only "see's" the nutrients right next to it), and then press with a roller of some sort (then lightly water). They make these for riding mowers, or you can do it by hand with a large object (sand bags work great for small areas, my personal favorite was a large inflatable jumping gym for the kids that came in a sack that I just covered with trash bags and rolled like you were making a snowman around the yard (backbreaking but faster than you would think). This puts the seed in direct contact with the soil and helps to keep the seed in place during wind/rain that would otherwise clump the grass and leave bare spots.

If the fertilizer he put down contains weed killer, then you probably will have problems with germination, and if it contains a preemergent, then you definitely will have problems. If it's just regular fertilizer, large or small granule, then it shouldn't be a problem. Starter fertilizer contains larger amounts of phosphorus and potassium in addition to nitrogen, as opposed to regular lawn fertilizer, which is mostly nitrogen. Fortunately for you, the seeding window for Virginia runs till the end of September. You need to find out if he did in fact use a fertilizer with weed killer, or preemergent. If he didn't, then something else is causing your lack of germination.

That's not a test I'd use with any confidence. Some seeds float simply because they are so light for their size. I recently started some callirhoe. These seeds came from my garden rather than a commercial package, so I was really concerned when they ALL floated when I poured the hot water over them. (They need a hot water soak prior to cold stratification). In fact, even though I knew the floater test isn't foolproof, I panicked and ordered some commercial callirhoe-- and then my personal seeds germinated upon removal from cold stratification. So, I guess I'm going to have lots an lots of callirhoe! The same is true for rose seeds, btw. Floaters germinate at a lower rate than the "sinkers," but many do still germinate, so I no longer bother to separate mine out.

I suggest ebay sveral venders have mixed seeds at good prices ( Rob at nishikimapleman has them nishikimapleman@comcast.net )... "specific cultivar Varieties seeds" is a crock!!! as Matt says you can't be guranteed anything and will likely have to wait years to really know what you have and you can't call it any named variety ever ethically. Prices for seeds on ebay vary from cheap to stupidly expensive IE: 5 for 4.95 and a bigger crock are "bonzai seeds" now being promoted I guess when the sprout they also have a small pot and root prunning sizzors attached ;>)...If I were you I would look for seedlings ...ebay does have good prices on those and your guranteed to at least see them alive for a month or so ;>) and pr plant they are prices coompetitive with seeds that may or may not germinate...Even with properly stratified seeds (??????) your germination might be 25-50% maybe more but I'd guess unless you have a perfect enviorment thats what you would get and of those some will die after sprouting ... anyway thats my take ..BONZAI SEEDS ...that one takes the cake!!! David