Where to advertise:
Websites: ebay has most problems with high-turnover items such as cheap to mid-range hifi, cars etc Problems are significantly less for specialised hi-end stuff. But I believe that eBay insists on working through PayPal so your preferences there may remove this option.
If I wanted to sell some good camera gear, I would advertise on a specialist website such as this one and if you get a response from an active member with several hundred posts to their name then all the better (like-minded individuals are less likely to pull one over on you).
Selling over wbsites, you can meet timewaters. The guy who says they want it then dither for weeks claiming they are 'getting funds together' and then pull out. Not common but is a real pain in the @ss when it happens.
Another option is to sell through a shop. Some shops will put it in their window under their own name and pay you when it is sold (maybe less a comission) or will advertise it on their website; I think this sometimes gives a better price than them buying it from you outright (or part-exchange) but it depends on how quickly you need the cash.
And be honest about the quality. I don't like describing something as 'perfect' because my definition of perfect may not be someone elses. It depends on how confident you are about it. Explain what accessories are included and whether you have receipts, warranties, orignal packaging etc as these can boost the price.
Scam responses - I don't know about USA but in UK we have heaps of scams from Nigeria and when they reply to an advert it is often quite easy to spot that it is not quite right. It is hard to describe in a foolproof way but when I first got one I knew immediately (poor English grammar, entreaties to God and over-enthusiastically wishing you good health etc). With specialist gear (and it sounds like some of your will be) then you will often find they ask questions out of line with what you would expect from a genuinely interested potential buyer.
PayPal has come under increasing fire for its practices (eg http://www.paypalwarning.com/)
so I am not surprised you are cautious.
The ideal is, of course, cash payment - the buyer comes to actually see the gear and hands over wads of paper for the camera. Offers of 'can I take it away now and bring the cash tomorrow' should be avoided. Similarly if they give you a cheque I would insist on the cheque clearing first (cancelling cheques is not unknown).
There are always problems with cash transfers/cheques - do they want the goods before releasing the funds or do you get the money in your account before sending the goods? A banker's cheque is more reliable than a personal cheque and money order is (in the UK anyway) at the same level.
Money transfers - great if you can do it and often the more secure long-distance purchase. But if the name 'Western Union' is mentioned then walk away. Not that WU itself is corrupt, but the way they operate mean that it is used widely by scammers.
Another classic is that the potential buyer explains they are owed money by another person (or company) and that this person will pay you as a way of cancelling all or part of the debt. As if that is ever going to happen....
Whatever terms you want to follow (cheque clear first etc) I would make it clear either in yor advertisement or over the phone/e-mail at the first contact so there can be no argument later.
I would be hesitant about offering a return policy for the reasons you mention - it can be hard to sort out who has done any damage. As long as you say on the advert that you have done your best to clean it etc then I don't think that they have cause to complain.
Damage in transit can be a real pain - sometimes the buyer says the seller sent them a damaged article, the seller says it was the courier. This is partly the reason that having the original packing (box and styrofoam) boosts the price of second-had gear - it can be shipped as safely as the manufacturer originally thought was sufficient (plus you can add a bit more packaging yourself). Even if the buyer insists it is damaged then do not return funds until they send the camera back; preferably with the original packaging so you can see how badly it has been handled in transit. It may help if the buyer cn take a photo of any damage and e-mail it to you. This will also help you claim against the courier/postal service for any losses.
Overall, there are loads of things that can go wrong and you can drive yourself paranoid worrying about them. Follow the course you are happy with and take all sensible precautions.