Depends how risk averse you are.
We have done a private villa with pool in Spain every summer, bar this last one (Brexit...) for 8 years. And ages of the DC.
We find the villa ourselves (OwnersDirect, usually); then find the flight, Flybe, local to us; Hire car last. Small SUV. Research which companies are scamming customers, avoid. And make a big song and dance about photographing the car when you pick it up; point out every scratch! We've not been caught out, yet.
Usually the villa people will hold the villa for 24 hours while you secure your flight. Remember to delete cookies from your PC so your flight doesn't rocket in price once they know you're interested.
The once we deviated from this was our least favourite holiday; Thomson in The Algarve (so not Spain!). Included hire car was a Fiat Panda; brochure evasive about air-con (struck a deal with the quite intrusive owner/pool guy who actually turned out OK- he was there often enough!).
It's always a risk. Review, review, review. Find the villa on multiple sites. Contact the owner early. I physically find the property on google earth and innocently message the owner so they know I know where the villa is! It's time consuming but the sense of achievement when you nail it
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So far, so good for us!
My family are very antisocial
. A private villa with pool (and aircon bedrooms) absolutely works for us. We started with a last minute 7 days to Majorca, 8 years ago, after a washout of a camping trip to Dartmoor; the last was 14 days in the Altea Hills.