I can't comment on "enviro phone" As I have no experience with it.
But eBay is another matter; two things I have learned (at the college of hard knocks, of course):
1. I find out what the UPS shipping charge is from my location Albany, OR to the east coast. (this gives a sufficient amount to not get caught with a lessor amount like the eBay shipping calculator did to me to the tune of $16.00 because it can not cope with two items in the same shipment!
I then get the buyers zip code and find out the exact shipment cost and use that on his invoice!
2. eBay you have to set a minimum price. And I determine that by searching for like items on eBay. Otherwise I use 50% of original price.
3. But you are right in the final analysis, eBay is a pain. I like craigslist much better, when the buyer comes to you. No shipping, a bit of hagging of course but at least you have a "live one"!!
45yrs professional photographer