How to make your first sale at agon

This is a very dicey situation and you can argue on both sides.

Do you have any other sites that you have sold stuff on? You can refer to that. I suggest that you start with a low value item first. That way, if a reputed buyer wants you to first send the item (and then make payment), then you can take that risk and hope that things can go well. Obviously you don't want to send a $2k amp without getting the payment first. Even with the low priced item you would not sell it to a person with 0 feedback, especially if that person has joined within the last month. But if there is another poster who is active on this forum for a long time, but has 0 feedback, you might want to take a chance.
When you create an ad, make sure that you have big pictures which CLEARLY show the condition of the product. Try to gather as much details and possible and be as honest as possible. Even if you feel the item is 10/10, make sure that you put it as 9/10. Just an example. Think of it - if you were to purchase from this site, what would you expect from the seller? It's all your Karma. I was in the same position years back.

Your involvement on this site, as indicated by your profile as "since 2011" is the only positive ting going for you. Fortunately or unfortunately, for you, that amp is a "hot pick" on this site and with reasonable asking price, it will be snagged in a few days. Good Luck!

I am sure there will be others to chime in.

If your item is well described and priced reasonably it will sell. Grade very conservatively and don't attempt to nickel and dime on PayPal fees, shipping etc (ideally offer free shipping in the continental US for example)

In other words make it as painless as possible for the potential buyer to work with you. And consider a link to this thread as well to indicate your bone fides and interest in doing things right!

I have had good experiences, buying and selling on Audiogon.

I'd say it's OK to exchange emails on Audiogon before a formal offer is extended on the site.  But I would avoid dealing with a buyer who wants to consummate the sale outside the site.  I had one guy who emailed me thru Audiogon, asked me to call him, which I did, and we went back and forth on the phone, came to an agreement on the price (which he said he'd pay in cash), then when he arrived in my driveway said that he rethought his offer and wanted to buy the unit for $600 less than we agreed upon.  With no formal offer on Audiogon, there was no "trail".  I wouldn't deal with people like that.

How did you guys make your first sale? 

I posted a for sale ad in the marketplace.

Pictures and details help, but for the most part, price seems to be the most important part to most. Price it attractively, and it will sell quickly.

Generally, the market will determine the price, regardless of the seller's experience.
Price it too high, and it can linger for months, or years even.
Price too low, and it will be sold within hours, but you may short-change yourself.
Price it right, and it should be sold within a month.