Oh....my....god.
1. Check your email, he told me he has emailed you twice since last you responded, yet you refuse to respond. The few times you did respond, it appears you were rude/sarcastic.
2. When someone requires cash for a sale, it's to protect their own back. It is ABSOLUTELY not uncalled for or unheard of to call for cash. I wouldn't expect any sane person to accept a check, give the buyer your stuff and then hope to god that their check clears in the next week.
3. The seller is a personal friend of mine for the last 10+ years. He rarely sells his possessions. He's the most honest person I know. You may ask why he doesn't have his receipts: we both bought cameras together over a year ago for a photography major at OSU, in which case both of us have switched from. At that point in a college career, why would he think to keep his receipts? (Canon and Cord Camera stores have always been helpful and responsive even to me, who also has no receipts for his equipment.)
4. $800 is a great deal. It isn't "half the price" of used camera gear. Obviously the items here have depreciated, but he just wants a quick sale. If he sold on eBay, he'd get raped with seller fees and shipping/insurance.
5. Also, I believe he would accept cashier's check or money order, yet you still deferred. Sounds a "little" suspicious.