OK.....there are without doubt a number of issues on the site that basically relate to customer confidence and also (from a UK perspective) DSR issues that really do need to be addresssed.
Design elements are also important as has already ben mentioned and are again worth looking at. The more professional that you can make your whole operation the better.
As I previously said, I think that your current marketing spend is wasted and you need to dump low grade media that bring low quality visitors and no real buyers and opt for proven media using highly targeted ads with direct landing pages - rule of thumb being potential buyer of a particlar product sees your ad, clicks thru to the exact page with that product on, good product info and lots of "buy me now" and that will have a real impact on your conversions. Include as much info in your ad as you can including the shipped price....you want to attract buyers, not visitors....many people fall foul here by inviting people to have a browse...thats not want you want....you want people to click thru (bearing in mind that you are paying for that click) knowing exactly what they will see and how much it will cost.
As for Paypal...I have to disagree with the previous poster. Whilst Paypal "can" be seen as a bit "ebayish" it still has its merits and is trusted by many buyers plus there is the big advantage of people impulse buying when Paypal is offered..... Paypal users almost always know their passwords by heart and can make an immediate purchase whereas people tend to have to go and find their credit cards to type in the detail....realistically that can be a barrier, albeit a small one.
I think it is a little confusing to some people here as the OP is a US site owner with a US site for US buyers..... so things like dollars etc will be obvious to the OP's target market... i.e. Americans in America, in much the same way as we say Pounds assuming that everyone understands that we mean British Pounds as opposed to Eygptian Pounds or whatever.
Anyway, just a few thoughts that hopefully might help.