this is far too long for. I have a better way I've been using since I started playing skyrim due to a xbl friend telling me and I've never heard it mentioned in the vids so I thought I'd let you guys know. sorry in advance if you already know this, this is for the people who dont.
Anyway, after selling what u can to the merchant and he's at 0 gold, save ur game, kill the merchant then load up the game u just saved and the merchant u just brutally murdered will be back behind the counter with a fresh batch of gold and a totally fresh batch of goods.
So even if u ain't got anythin to sell and ur just after more arrows, ingots or potions etc. Then just repeat the process above for a fresh batch of goods aswell as gold everytime.
Simple and much quicker than waiting 48 hours everytime.
Hope this helps as much as it has helped my 3 characters throughout there journeys through skyrim.
once again sorry to the veterans who will no doubt know this already and will have for ages.
Enjoy!

There's a YouTube video for everything you don't want to know so how is something useful not on there? 
