Combining multilpy items and getting the new purchases to show up so he could fix them before I paid

[annscollectables65]

I made an offer and he took it. I asked him if he could combine another purchase even before he accepted my offer. He said yes and I told him which item I was wanting and he said to purchase it and he would only charge me one shipping. I could not get the new purchase to show up where he could find it and add it. I tried everything. I went a head and paid for the first item. I had to pay for the second item with the shipping because I could not get it to show up on his side before paying for it. He is going to refund me the shipping, but what is wrong? Why is this happening. I need help because I would like to buy some more things in the next few months.  Thanks