Currently bartering/attitude affect both sell and buy price. If I don't want to spend gold right away I'm better off stashing items and selling them later when I have more points in bartering and higher reputation. This is annoying and doesn't add anything to gameplay.

If Divinity Wiki is right, the price ratio at 0 bartering/0 attitude is 0.4:2.5 (you sell items for 40% of base price and buy for 250%), i.e. 1:6.25. Well, why not simply make it 1:625?

Game economy won't be affected at all because the ratio will stay the same. And at 5 bartering/100 reputation it'll be 1:1 just as it is now. However, trading in early game will be more comfortable because players won't be punished for selling items instead of stashing them and selling later.