Cancelling order due to suspicious buyer

[timetoshop001]

I recently sold an item for $150 with free shipping.  After the buyer agreed to purchase it by making a best offer that I accepted, the buyer started asking questions like when was the item manufactured?  I responded, but that seemed like it should have been asked prior to sending me a best offer. Then the buyer begins to ask that I ship the item a certain way so the post office doesn't charge him a lot of money.   I explained that it would be shipped in a USPS large flat rate box as it is heavy and won't fit in a small box, but I will pay the shipping and there shouldn't be any cost for him/her.   I checked the buyer's feedback and while it doesn't show negative or neutral ratings, if you read the comments there are several about him not paying, a few about him running a scam.

Now I'm concerned that he is running a scam and will get the package and say it was empty or something. Contacted ebay and they said I could cancel the order, but it would negatively affect my seller performance. Also, wondering if I can still get a final value fee credit if I cancel the sale???  This will be the first sale I've cancelled, I've never had any other situation like this, so I'm not sure what to do.  Seems unfair that my performace rating would be affected when I'm thinking this buyer is running a scam. Still, I'd rather have a little negative than be out $$$.