eBay

"their fees should be based on sales price "

It is, the total sales price. What the buyer actually pays for the item and that includes taxes & shipping costs. It's the same as if you bought it from a store. For example: The retail price of the generator on the shelf has the shipping to the store, taxes paid, etc. built into the retail price on the sticker and (if you are a sales tax state) more tax. eBay is just a big store that shares it's info because it's participants are both buyers & sellers on the same venue.

BTW: The buyer does pay 13.25% of the added sales tax.

I haven’t had any problems with eBay and I’ve sold and purchased quite a bit. They charge their commission and my state sales tax. I don’t see what’s wrong with that. It’s mind boggling that they can expose your items to a huge audience of buyers interested in just what you’re selling. And that’s what you’re paying for. If that’s not a good deal for you sell your things another way. 

@thedoc2004   List  on AudioMart where it is free.  I have sold every item I have ever listed on that site.  Why pay any fees when there is a site dedicated to Audio equipment.  Ebay may give you exposure, but AudioMart gives you exposure to the right audience.  IMHO   

The OP's point about eBay being unethical in the way they charge their fees is understandable but I look at it a little differently. 1) The fee structure is transparent; it is in their user agreement, 2) As pointed out above it circumvents any games a seller might play with pricing and shipping, 3) If eBay didn't charge a percentage on shipping and sales tax they would just raise their fee on the price of the item. Instead of 13.25% perhaps they would charge 15%.

I've sold quite a bit of stuff on eBay over the years and even though I'm irritated at some of their policies, I continue to use them. One of the most important benefits they provide is that they have negotiated very attractive shipping rates. If you book you own shipping you will see that it is much more expensive than going through eBay.

You may have a complaint about charging fees on shipping and taxes but IMO the fee that eBay charges compared to the service they provide is still a bargain. I'm old enough to remember the days before eBay when selling a piece of stereo gear was a big hassle. You took your component to your local stereo store (if you had one) and stood there powerless while they offered you 20% of its value if they would take it at all. Your only options were to put it in the closet or take it to Goodwill. So you took a deep breath and mumbled "OK." Paying around 15% or so to achieve an honest auction value for an item is a much better alternative in my experience.

eBay becomes super greedy with their charging tactics 

overall eBay charge 15-16 percent fees and tax every item I sold 

the sad part people don’t understand how  eBay charges both ways seller and buyer 

seller pay fees and tax buyer pay only tax