Killing wild yeast question

I've noticed that most of the sites recommend when starting with fresh grapes or juice etc to add agents to kill wild yeast before adding a yeast packet. Most of my wines until recently have come from fresh juice pails from a local shop who recommends using the wild yeast (which I mostly have in the past) instead of the packets. He sells the packets as well but never recommended killing the yeast in the pails. I started 3 carboys with natural yeast and three with added yeast in September to see if I noticed a difference but didn't kill the wild yeast prior to adding the yeast packets. What are the dangers of doing this? I've done some in the past the same way but never did a side by side comparison as I'm doing this year. My wine has always turned out without killing the wild yeast but maybe not as good as it could have I guess. Could it be that since the juice comes from a reputable supplier and maybe it is actually yeast injected like I have read about and it's not a wild strain at all? The big difference I have noticed so far is the yeast added carboys are not as clear as the wild yeast carboys looking at them side by side. If this might be a problem is there any soulutions?Thanks in advance, Ken

Ken, most modern yeasts used in kits are selected for both the variety of the grape and also for their very agressive nature and I tend to use these yeasts in my country wines and meads as well. Certain modern yeasts, made by both Red Star and Lallemand, are so agressive they will literally kill any wild yeast that may be present. I never use k-meta any more prior to primary fermentation to kill wild yeast since the yeast I choose will take over and become the primary strain.

For Lalvin yeasts, some of the more aggressive common strains are EC1118, KV1116, and D47.

Thanks, the juice pails dont come with the yeast but he sells them at the shop, I believe the ones he sold me for my Cab and Merlot were premier cuvee(have to check my notes) and the one for my Pinot may have said Bouvign or something (once again I need to check my notes) you can tell I dont use the yeast packets much lol. I'm hoping all is well with them, I think I'm reading too much, Ken