Scent control WORKS! Now, I'm new to Coyote Hunting, but not whitetails. Since starting to use scent control (Which I'll define) I see many more deer, and the deer are MUCH more calm.
Scent-Loc is not a cure. Its a tool, over rated or under-rated I'm not sure. The key to scent control is a full system.
Firstly, take scent free showers - meaning use unscented, soaps, personally, I prefer the fresh earth scented soaps. I do use the "hunting" soaps, they really don't cost that much considering how long they last. I also use unscented deodorant - Right Guard - its cheaper than the hunter stuff. In addition, during deer season, I always trim my under-arm hairs, and chest hair. I don't shave, but just use clippers.
ALL of my hunting clothes (including socks and several pair of underwear) are stored in a plastic bin. I NEVER wear them out to eat, at a gas station, or anything like that. I don't leave them laying around the house. When I return from hunting, they immediately go into the bin. These clothes are washed ONLY with scent free soap. I use ALL Free & Clear. Seems to work the best for me. If I want a cover scent, I use Knight & Hale Fresh Earth Detergent.
I wear knee high rubber boots, and spray them with scent eliminator before entering the woods. There are plenty of home-made recipes for scent eliminator.
The Nay-Sayers here are right about one thing, you can't ELIMINATE your scent. But think about what you are doing. You are reducing your scent to the point, hopefully the animal that smells it might thing you are 3x or 4x further away from them than you really are. Your scent trail smells several hours older than it really is.
I mean, how long do you think it takes after you've walked in the woods, before a Coyote WON'T run when it comes across your scent trail? 1 Hour? 2 Hours? 24 Hours?
With whitetails, it makes a HUGE difference. You don't trick 3-1/2+ year old deer without some form of scent control. I'm not saying run out and buy a $350 scent lock suit. I'm saying, take a scent free shower, wash your clothes. Don't put your hunting clothes on then cook or go out to eat breakfast, roll around with your kids and dog, and then pump gas on the way to your hunting spot....
As far as gun-oil, burned powder etc. I'm not sure about that. I'm primarily a bowhunter and can keep everything mostly scent free. Considering Coyotes get hit by cars, its obvious that the smell of exhaust fumes and vehicles doesn't scare them too much - or they wouldn't get near the road. Other than that, I don't really know....
In my opinion, scent control does work and its worth the effort!