Besides a lot of letters, Lodewijk Wesselo also wrote a brief autobiogrpahy (2 pages). In it, he describes his career, among other things. He tells briefly about the time he was the manager of a store in Middelburg during the period 1912-1920. He sold jewelry and objects made of precious metals like gold and silver. He wrote about this store: "thanks to the First World War, the business florished."
I found this to be a rather strange statement. To my knowledge, the Dutch economy took a heavy hit during the First World War. The Netherlands were neutral, which made all countries that were at war hesitant to trade with the Netherlands, afraid as they were that the goods they exported to the Netherlands would fall into enemy hands. Since the Dutch economy is heavily dependant on import and export, it took a heavy blow. Even later on, when trading with the countries like England resumed, it was under heavy restrictions to prevent anything valuable from falling into German hands.
So how could a high ends good store do so well? Base materials to make the products were almost impossible to get during World War Two, and I expected it to be the same during the First World War. Not to mention that many people wouldn't have had the money to buy anything on offer in the store.
I asked for clarification on this issue on a Dutch forum devoted to the First World War.
The first part of the answer came from one reply. During the First World War, there were a lot of Belgian refugees that came to the Netherlands. This person suggested that the Belgian refugees were perhaps selling their valuables to get some form of income. Since Middelburg is close to the Belgian border, it's very possible this was happening.
The second part of the answer came from someone else, and was in hindsight so obvious I should've thought of it myself. His reply to my query was that in times of crisis, people invested in valuables like gold because the value of that is much more stable than the value of money. So there we had the sales part.
Lastly, one of the moderators gave me the link to a book with several essays about the economy in the Netherlands during the First World War, which was an interesting and enlightening read.
So my thanks go out to the lovely people who responded so very quickly to my question. I learned a lot!