Three things determine what an international transfer actually costs you: the exchange rate spread, any flat or percentage fee on top of it, and how long the money takes to arrive. Providers optimize these differently, and the cheapest-looking option on one dimension is often not the cheapest overall.
Start with the total received amount, not the advertised fee. A transfer service charging a flat $0 fee but giving you a rate 2% worse than mid-market will cost more on a $3,000 transfer than a service charging a $15 fee at a rate within 0.3% of mid-market. Compare providers by converting the same amount on each and seeing what actually lands on the other end — most transfer services show this before you commit, so use that number, not the headline fee.
Speed and cost usually trade against each other. A transfer that settles in minutes typically costs more, either through a wider spread or an explicit express fee, than one that takes one to three business days through standard bank rails. If you're not on a deadline, standard transfer speed is usually the better rate.
Recipient bank matters more than people expect. Transfers that arrive as a local bank deposit in the recipient's country are usually cheaper and faster than transfers that get converted twice — for instance, sent in USD and converted to a third currency by an intermediary bank before reaching a local account in a different currency. If you can send directly in the recipient's local currency, do that.
A few specific things worth checking before you send anything meaningful:
Whether the rate you're quoted is locked for the transaction or floats until the money is actually converted — rates shown at the start of a transfer aren't always the rate you get if the transfer takes days to process.
Whether there's a minimum or maximum transfer amount that changes the fee structure — some providers charge a much higher effective percentage on small transfers because a flat fee is a bigger share of a small amount.
Whether the recipient's bank charges a separate incoming-transfer fee — this is common and rarely disclosed by the sending service, since it's not their fee to disclose.
For recurring transfers — rent, family support, business payments — even a small percentage difference compounds fast. A 1.5% spread difference on a $1,000 monthly transfer is $180 a year, which is real money for something that only takes a few minutes of comparison shopping to avoid.