Frankly, I'm of the opinion that being overly fearful of being scammed is a detriment to yours or any one else's eBay selling carrier. Let's face it, it takes some guts to be in any type of business and as the saying goes, "never let them see you sweat."
By "...offers well over the asking price" are you talking about offers being made on fixed price listing items or those being sold at auction in auction style listings? In the first I would be extremely wary of someone offering more that my stated price and put them on my BBL immediately without further communications with them.
On the other hand, if this is an auction style listing that has the BO option attached to it, the starting price that you set is not the asking price but merely a starting point for the bidding. In such cases it would be reasonable to offer more than the starting bid price. In fact, if they didn't offer more than that I'd probably block them as well for shear stupidity.
One thing that you need to remember about offers made on an item being sold at auction. That is that once a bid has been placed all offers become void and you can no longer accept them. The ones making such offers would then have to bid on the item through the normal bidding process. The selling price being determined by the bidders in competition among themselves. (Oh! It should be noted that any offers made would not automatically convert to bids and so those that made the offers would have to place bids themselves.)
By the way, you don't have to explain why you decline an offer. Frankly, I wouldn't. Remember, they can smell fear and inexperienced seller's usually have quite a bit. The trick is not to show it.
"It is an intelligent man that is aware of his own ignorance."
