Purchase order, unknown merchant, buyer protection

[mBioGen]

A seller I don't personally know has sent a PO through PayPal for a high value item (over $4500). Should I complete the perchase?

[kernowlass]

@mBioGen 

Why would a seller send you money? Normally buyers send money and sellers receive it, or is it a refund?

Whats a PO? Postal order?

Are you selling something, are the funds showing in your paypal balance?

A few details would be good if you want advice.