The first time I went to a coin dealer they had a set price of how much I could get in the first transaction. In order for me to buy from the coin dealer my purchase had to be 1500+.... On eBay the only con is making sure you are buying from a credible seller, which you can find out by looking at the sellers feedback. Overall good feedback is how to find good sellers on eBay.
Some dealers do have a limit but its a lot rarer now.