This is another avenue which you can look into when you"re starting your hobby off for the first time. With this option you won"t be able to hold your new coins in your hand until you actually receive it in the mail, but at least you know that you"ve made a purchase and that it"s on the way to you.
And yes, just like in any other way that you might get your coins, through mail order you can also get bad coins, but here you"ll want to be especially careful since you don"t get a chance to view the coins first before you buy it.
You have to take it on their word that what you"re getting is the real deal. The best thing that you could do therefore if you"re going the mail order route, is to first buy coins which won"t break your bank balance.
Another good practice when buying through mail order is to stick with certified coins and mint sets. Bullion should be alright too, but I wouldn"t really advise going anywhere near rare coins. Modern issues are a much better investment through mail order than older rarer coins.