This isn't something which can be answered by others easily. You've done your research on the display, and if this is what you want, then picking a seller to buy from is up to you. One-off shops which sell below the pricing of others should always be questioned. You may not have a warranty on it if LG doesn't allow for third party sellers. You may get the wrong product, like the 55" version, then what do you do?
If Amazon is going to stand behind the seller, then I'm not sure if you really have an issue, but Amazon doesn't always do that with every seller.
I purchase from Amazon all the time. I've purchased televisions and projectors and other big ticket items. I've never had an issue.
But, I've never purchased from a thrid party seller.
Certainly emailing them shouldn't be an issue. But, considering that there are very slim margins on most televisions sold (10% - 20% markup), it's an unrealistic price. So, it's likely a typo. That is, it's probably the 55" or there is something else going on.
In most cases of incredibly low prices, there is some scheme to get more money from you or the order doesn't ship to you. I get the concept of saving a few bucks, but I also want acceptable return policies, the product I actually ordered, and support if something goes wrong with the order.
Start with that email, it will give you solid insight into what to expect. If they end up trying to run a transaction outside of Amazon for this, then something is fishy.