Why Does PayPal Charge a Fee to Receive Money?
If money landed in your PayPal account for less than you expected, the payment was sent as goods and services. That payment type charges the receiver a fee of 3.49% of the total plus a fixed $0.49, deducted automatically before the balance hits your account. There's no version of a personal payment that charges the person receiving it, so if a fee came out, this is why.
The fee funds the buyer's protection, not PayPal's profit margin alone
Goods and services payments come with PayPal Purchase Protection for the buyer: if the item never arrives or isn't as described, the buyer can file a claim and get their money back. That protection, plus the payment processing and fraud monitoring behind it, is what the 3.49% + $0.49 fee is paying for. It's the same structure a credit card processor or marketplace charges for the same reason, PayPal is acting as the payment processor and the dispute arbiter at once.
You can't opt out of the fee and keep the protection
There's no way to receive a goods and services payment without the fee. Some sellers price their listings knowing the fee is coming, so the number they actually want to net is the target for the calculator, not the price they type into the invoice. Use the PayPal fee calculator to work backward from a target payout to the amount you need to charge.
Ruling out the other explanation
Occasionally what looks like "a fee to receive money" is actually a currency conversion, if the sender paid in a different currency than your account's primary one, PayPal's conversion rate (which includes its own margin) can shrink the amount you see land, separately from the 3.49% + $0.49 fee. Check the transaction details for a currency conversion line before assuming the fee itself was miscalculated.
For the exact fee on any payment amount, see how much is the PayPal fee for goods and services. If you're the one sending, not receiving, see does PayPal charge a fee to send money.