Yes you are correct;
They check out my stuff on e bay and by on Gumtree and pay around 15% less.... While listing on e bay is free, i may continue to do that with certain Items.....
I however only sell new items on Gumtree; sort the non serious buyers from the serious on gumtree by stateing sales only go through paypal and offer postage / shipping as an option at a competive rate... also i state all sales are refundable and protected by Pay pal... and if the buyer contacts me by phone directly, I may be flexible....buyers can come and look but the item will not be taken off until purchase is made.... usually If they want the item ... they pay through pay pal.
Over the past 2 months gumtree has represented around 30% of my sales and E bay 50%; other 20%
Yes I am also looking into my own site should I decide to become more serious.
Right now trial and error