Where can I buy a vintage silver coin?

Could you please elaborate on where exactly one might find and purchase a vintage silver coin? Are there any reputable online marketplaces or physical stores that specialize in such collectibles? What factors should one consider when choosing a vintage silver coin, such as rarity, condition, or historical significance? Additionally, what precautions should be taken to ensure authenticity and avoid potential scams? I'm particularly interested in coins from a specific era or country, so would it be wise to seek out experts in that field for guidance?