Before going any further, it is worth defining a term: spread. Because there are actually several stories behind the same word.
First, there is the ask-bid spread, the difference between the buying price and the selling price. The more liquid the market, the narrower it usually is. A wide spread means someone who buys and sells straight away will lose money. The wider the spread, the more the investor loses. Nothing crazy.
But there is also an artificial spread, which can be created by a broker and its various middlemen. For example, a share quoted at €50 to buy can end up more expensive on a trading platform, because it does not have the real-time quote, because it pays middlemen… or because it decides the price itself.
And all of this is perfectly legal: the spread is not considered a commission. It is a subject regularly called out, so much so that in 2021 the AMF, France’s financial markets regulator, published an article for savers1 telling them to read the contracts and execution policies. Which obviously nobody does, because they are:
As always: regulation only protects those who write it.