My payment perspective is somewhat limited by having always been a buyer and never a seller on AudiogoN and by not using Paypal. As a buyer I have, with one exception, used cashier's checks. To reassure the seller, I always state in my e-mail that I have no problem with delaying shipment until funds have cleard because I'm not in a huge rush to get the item (true). I think the seller can also be reassured by the substance and style of your communication.
As mentioned by several posters above, the remaining negative for a cashier's check and any other form of payment, compared to Paypay, is the seller's uncertainty until the payment arrives as to whether the deal will actually go through. If I use mail, I tell the seller I will mail payment no later than the day after the deal is made. I have also used express mail or one of the private overnight delivery companies when the extra cost of the service is relatively small compared to the amount of the purchase.
The cashier's checks of BofA, which I use, have a statement printed on the back of the check that information about the check can be had by calling a given 800 number. I called myself to test it out - the service verifies the check's authenticity and its payment once that has occurred. It's a nice feature because the seller doesn't have to spend time looking up the contact information for the bank and incurs no cost for the call. As to Blindjim's concern that the telephone number might be just another part of a scam, it's not likely a small time scammer will spend the time and money and disclose the information needed to establish an 800 number.
The one time I did not use a cashier's check, I deposited directly into the seller's BofA bank account, as mentioned by Ckorody above. No fees and it is fast. The seller had on-line banking and saw the deposit hit his account within an hour after I made the deposit. As to any risk that BofA might later unwind the deposit, I believe the Bank requires that the deposit be covered by cleared funds in the account of the person making the deposit. I don't know who would bear the loss if those supposedly cleared funds were later determined not to be good.
As a buyer, the one feature of Paypal that appeals is ability to challenge a payment when it is made by credit card. However, I have seen ads that specify Paypal payment be made by a means other than credit card, probably for this very reason. I've been lucky so far that all the items I've bought have been truthfully represented and not damaged or lost in transit, so I haven't had to seek a refund. If that happens, I may start using Paypay.