If you're looking to "trade" silver (insofar as a stock market trader "trades" stocks), you might find you're better off with unallocated holdings that can be added to on dips, and sold on peaks more readily than holding physical (and I say this being an absolute OCD nutcase about being able to hold what you own).
Physical attracts a decent sized premium based on production/refining and minting costs that is generally (at least as far as I understand it - I've never actually sold any gold or silver in my life!) lost at the time of sale, and thus, market needs to move significantly more in your favour in order for you to make a profit.
If your question relates to holding physical long term, and selling when you're ready, I would advise that during the time of accumulating silver and/or gold, you establish a good relationship with a few bullion dealers (you're likely going to be buying product from them anyway) - these places you deal with regularly will be the prime candidates for places to approach for selling some/all of your stack when the time comes.
