What fee am I paying? (aka can you explain what binance charges clearly)

This is what usually happens:

1. I go to card deposit which right now is free.
2. I deposit 100 euro
3. I go in the wallet section and I can see they took no charges and that I have 100 euros.Now the great part comes. I'm attaching a screenshot of a purchase I did with those 100 euro on ADA/EUR.

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https://preview.redd.it/8c9owazp3vi71.png?287&format=png&auto=webp&s=1b0142c1971e063f489469d255878506c27f8302

1. I went into the market section and placed a limit order in the spot section so that I'd pay my 100 euro ADA 1.259 euro per each.

2. I've payed 0.0794 commissions therefore 0.0794 * 1.2597 means that I payed around 10 cents of commissions.

3. I go on the wallet immediately after the purchase and I find myself having 98.5 euro in cardano instead of 99.9 or something like that. And the strange thing is that I also made other purchases and it seems to be always something like 1.5 euro less than expected.

Is this a scam or what? At least they could make it clearer. Can some of you enlighten me?

Some mentioned spread here and there and if it might be something valid, it does not justify this amount of money (which is very big being more than 1% over the full amount)