A free plan and a trial are different offers
A free plan means the company lets you connect without buying a subscription. Proton VPN publishes one: one device at a time, servers in fewer countries than the paid plans, and the same Swiss company behind both. NordVPN, ExpressVPN, Surfshark, and CyberGhost publish paid plans. Some of them also offer a short trial in certain countries. A trial that ends and then charges you is not a free plan.
Match the store developer to the company site
Price is not a safety test. A free app with a familiar name can be a different developer using that name in a store. Before you install, check that the developer on the store page is the company named on the provider's own website.
Then read three pages on that site: what they say they keep (the logging policy), where the company is based, and what a free account cannot do. Device caps and a smaller server list are the limits you will notice first. A free app that asks to read your messages or your photos is asking for something a VPN connection does not need. The permission a VPN needs is the one that creates the tunnel.
Paid plans have two prices
The large number on a pricing page is often an intro rate for a one-year or two-year plan, billed up front. The renewal price is what the same plan costs when that term ends. Both figures are on the provider's pricing page. Compare those, not the intro figure alone.
The refund window is the practical way to try a paid app: subscribe, use it on your own network, and ask for the money back inside the published number of days if you do not want to keep it. Read the exceptions on that page. The window often applies to a first purchase made on the provider's website. Purchases inside the Apple App Store or Google Play often follow the store's refund rules instead.