I'm not really one for buying slabbed coins unless it's a question of authenticity, but to each his own on that. I agree that sometimes the size can be deceiving. You think because of the price or face value that it will be a crown sized coin and it's actually quarter size. It can be hard to find the silver content too. The mint will say how many grams it is I think, but that means nothing to me.
There is one good thing about buying on ebay. If you buy something that is not as described, all you have to do is request to return it and also ask for a return shipping label from the seller. Explain that this was not as you described it and you will get your money back and a lot of times keep the item as well because the seller does not want to pay for the return shipping. And even if he lists the item with returns accepted, buyer pays return shipping; if that item was not as described you won't have to pay a dime more out of your pocket. Ebay has got your back, because Ebay will reimburse you in full if the seller does not respond in a time frame that they set up.
I have a complete set of the Krause catalogs, the most recent versions, cost $110 shipped free, but oh so much information, includes silver content, size, weights, etc. An invaluable resource for collecting all coins of the world.
I buy slabbed coins online because at least someone has agreed on a grade. This is true to me since you don't usually pay anymore for a graded coin than a raw coin. I am very new to buying world coins so I was bound to get bitten eventually. I just like large silver coins with high silver content. I could just buy US bullion coins but that is too boring. I do buy Morgans, but some of the prices make me stutter.
O--M--G! I have nothing but contempt for the United States mint, yet this coin is so bad it makes their US counterparts look like artistic giants. That $15 coin is so ugly, I suspect it would be difficult to spend it for $15 in Toronto at a coffee shop.