1) You should INCLUDE as many pictures of your equipment to include the back of the unit, both side views, top of the unit, original packing box to include the insides, Unit brochure, Company Sales Unit brochure, remote, etc. If your unit has special feet (or anything else unique), please include these pictures. Most ads not include enough pictures.
2) Also, include background information on the company. You can copy some information from their web site to help people know who the company is. A short paragraph should do the job so use your imagination.
3) Your unit is a wonderful great sounding audio component and you need to include information on its features and benefits. More descriptive info on your unit is suggested (most ads are too brief).
4) Include details on how you are going to pack the unit amp for shipping. If possible, include pictures of the packing box, inside the box and other details. You need to give the buyer confidence the unit will arrive safely. It is very important for your buyer to understand how your unit will be packed and shipped (FEDEX, UPS, USPS, Freight, etc). Explain how the shipping and insurance is going to work (including the units insurance value) and who pays for it.
5) Do NOT be afraid to counter offer any low ball offers received.
6) If your item does not sell in 30 days, you probably should lower its asking price and maybe even improve your descriptions and pictures. Or, after 2 weeks, you could lower the price, etc. The lowering of your price depends on how badly you want to the sell the unit and what responses you are getting on your ad. If zero responses (meaning no questions), maybe it is time to lower its price, change the pictures and descriptions. If no sale within 30 days, you can always re-list and see what happens. There are no rules for this so use your best judgment or ask your friends for advice.
7) You must promptly answer ALL questions received with accurate and informative answers. You can always include additional information, if appropriate, trying to be a consultant to your possible buyer. Sometimes it is useful to exchange phone numbers if a discussion is required (you decide).