Is there a way to tell if an App is free before downloading it?

Apps that are marked Get, and only Get, are free.

Apps marked as Get with In-App Purchases next to it are free to download and use, but will be limited in their use. That can mean either you pay for a subscription to continue using the app at all, or you make various one-time purchases within the app for extra features.

One-time purchase apps will show a price rather than a Get button.

Edit: Oh! And here's a new one (at least to me it is). I clicked on a version of Angry Birds marked Get. Okay, it's free, right? Uh, no! You click on the Get button, and instead of downloading the app, you cannot in any way get the app without agreeing to a 3 month trial of Apple Arcade, which then turns into a subscription.

Stick with the Get and only the Get button without the in-app Purchases note next to it. Most developers do have in-app purchases in their apps because it does cost them money to put the app in the App Store and also time and money to develop and continue to update the app. They are not just doing it out of the goodness of their heart.

You are likely to find very little options for apps that do not have in-app purchases, but some may get income solely from advertisements to offset their costs.