Rather than answer a question with a question I'll just answer your question.
No, it doesn't sound "scammy." It sounds like a vendor who knows their postal system is problematical, and as a consequence delays happen. You haven't gone into detail about the item, but if it arrives, say, months later and you still have a use for it you probably - from a moral and ethical point of view - should pay for it. If it's an item, say, that you needed for a project and you had to source a replacement item elsewhere I don't think in that circumstance you should have to pay for it. Some may argue that if it arrived months and months later you wouldn't be expected to pay for it because the vendor isn't in fact honoring the contract in terms of stated estimated delivery times. But why are you asking Club eBay to answer this question? Common Sense combined with your moral and ethical compass is all you need to find the answer.
