Jumping in here! Are you planning to shoot mostly indoors? I snagged a killer deal on an old Olympus OM-D E-M10 Mark II recently. It is super compact and absolutely fantastic for weddings!

Oh man, wedding pressure is the worst. Been there, done that. Honestly, with 600 bucks, your absolute best bet is going the used route because new gear is pricey and usually doesn't come with the lens you actually need. I've bought tons of gear over the years and you gotta stick to the reputable spots or you'll get burned. Check out KEH or MPB. They actually inspect everything so you aren't guessing if the sensor is trashed. Avoid random marketplace sites unless you can hold the camera in your hand first. For a wedding, you need something with decent low-light performance so you arent just shooting blurry messes.

• Look for the Sony Alpha a6000 24.3MP Mirrorless Camera. You can find these used for cheap and they have great autofocus.
• Maybe snag a Olympus OM-D E-M10 Mark II 16.1MP Mirrorless Camera if you want something super compact.
• Grab a cheap prime lens like a 35mm or 50mm if the budget allows, it makes a huge difference indoors. Dont stress too much about the gear though. Just make sure you get a reliable memory card, like a SanDisk Extreme Pro 128GB SDXC UHS-I Card, so your footage doesnt get corrupted. Good luck with the sister's big day!

If you are strictly working with a 600 dollar cap, you should look at the used market for a Fujifilm X-T20 24.3MP Mirrorless Digital Camera. It has a decent APS-C sensor that handles high ISO noise better than some entry-level options. Here is my take on getting the best bang for your buck:

• Look for a bundle that includes a prime lens. Zoom lenses in this price range often have variable apertures that struggle once the sun goes down at a wedding reception.
• Avoid chasing full-frame sensors. Glass for those systems will eat your entire budget immediately.
• Check sites like B&H Photo Video for their used inventory. They offer a reliable grading system and standard warranties, which reduces the risk of buying broken hardware. The Fujifilm color science is pretty solid straight out of the camera, so you wont spend hours color grading if you are in a rush. Stick to reputable retailers to ensure you get a working shutter mechanism.

Look, wedding gear is no joke and you dont want to gamble your sister's big day on some shady marketplace deal. In my experience, if you want reliability, stick to the reputable used retailers who actually check the gear. I have had zero issues over the years using MPB or KEH because they have a return policy and actually rate the condition of the stuff they sell. With your budget, search for a Sony Alpha a6000 24.3MP Mirrorless Camera body or maybe even a kit if you can find one. It is an older workhorse but it does the job way better than any phone. Seriously, dont worry about the latest tech; you just need something that doesnt crash when you hit the shutter. Make sure you grab a fast card too, like a SanDisk Extreme 64GB SDXC UHS-I Card. It keeps the camera from buffering while you are trying to catch the reception dance floor shots. If you have any leftover cash, hunt for a used Sony E 35mm f/1.8 OSS Lens. That focal length is a classic for weddings and gives you that nice blurry background look without costing a fortune. Just stay away from random auction sites with no buyer protection. Stick to the shops that offer a warranty, even if it is just a few months. You got this.

Regarding what #3 said about Jumping in here! Are you planning to shoot mostly indoors? I gotta be real with you, I had issues with those older micro four thirds sensors in low light. They just werent as good as expected when the reception lights went down. Unfortunately, wedding lighting is just brutal for older tech. Honestly, if you want something that isnt going to fail you, just go to YouTube and search for budget wedding camera setups. There is this one awesome video I saw a while back that breaks it all down perfectly, it should be like the first or second result when you search it. Also, just check the Reddit camera subreddits, they have these massive wiki pages that list exactly what to avoid so you dont get scammed. Spend an hour reading those lists and you will be way better off than trying to guess. Just keep it simple and dont overcomplicate the specs, good luck with the wedding.