The technique to this is really quite simple, it's just never really employed very often. This can work with any precious metals , of course. The only way this method won't work is if you're in a rush to sell all your precious metals, but how often does that happen?
Basically, you put up an ad about precious metals on any buy or sell site where you would then meet up in person. Sites like craigslist are obviously the best but if you live in Canada, there's a site called Kijiji that can be just as effective.
The reason why this method is so effective is because both the buyer and seller will be saving money. Regardless of if you were to buy or sell at an official precious metals vendor, they will charge you a few dollars above spot for buying or give a few dollars less if you are selling. That small margin between the two is how they make money. We can avoid this entirely by doing transactions with people directly, not stores. Obviously if you don't like meeting strangers, this isn't for you, but there's really no other way to buy or sell precious metals at spot price other than this.
If you're afraid that you may be conned when buying silver from a stranger, you can always arrange the meeting at a local precious metals vendor so they can verify it for you. I am sure the seller will have no qualms over this arrangement. If they do, it'll be really suspicious and you should probably not do business with him/her.