The seven highlighted words in the story all contain the letter H. However, the first word has H in the first position, the second word has H in the second position, and so on. This means that each set of seven words has to contain a certain letter in each of the positions.
The problem is that there are words that fit more than one group, some even as much as three. Not only that, some extra words fit into certain groups, so it's tricky at best to find which groups are needed. One strategy is to jot down all the words with a specific letter in it, and then try selecting seven from the group. If the highest bid is less than, say, 700,000 gold, then that letter can be safely ruled out.
HINT: The letters involved in these groups are B, C, D, G, K, N, P, T, and W.