There are many reputable online coin shops on the internet and it is safe to purchase silver coins online if you are purchasing bullion coins with no collector value.
The primary thing to be concerned with when you buy silver online is how fast your order will ship. Regardless of what store you buy from, you want to only order gold and silver bullion that is in-stock and available for immediate same day or next day shipping.
Most online coin and bullion stores will typically shop USPS Priority Mail in the flat rate box, which costs $20 for any weight, so long as it fits in the box. Don’t be fooled by shops that charge expensive shipping, USPS flat rate is the preferred way to go.
Typically you will not be able to pay via credit card. The transaction costs are just too expensive for most bullion dealers. Generally when you order silver or gold online you will secure your order with a credit card but then wire or ACH transfer your funds or send in a cashiers check.