I'm sure you get that question a lot but... How to buy a flute? I literally know anything about it.

I studied flute for seven years and have been playing for eight (at the moment I'm on piccolo). I don't plan on playing professionally or even solo, I'd just play in an amateur concert band like I do now. I need something to serve me well for a long time.
What would be suitable for me? Which brand, model? New or used? Where to find used flutes? I live in a little European country and I'm not really comfortable buying from eBay, for example, but I guess I'd do it if it's the best choice.

You'll probably suggest me to ask my personal teacher but I haven't been in touch with him for a year so it's a bit embarrassing for me. I asked him several times while I was still studying and he just told me it's too soon for me to buy my own instrument. So I just kind of feel like I'm getting on his nerves when asking...

Well depending on your price range it varies. If your range is in the 3000 dollar ( American) range and up. I would suggest a Haynes,Pearl, or Altus. If you can go upwards of 5000 than any of those plus Powell, Muramatsu,Sankyo, or Burkart. Any of those would last you for a long time. Go to the closest music store that has a good selection and try as many flutes that meet your criteria as you can. Or if you can find someone you know who has a flute you'd be interested in, ask them if you can try their flute and see if you like the feel. Some companies will let you arrange a trial period of their instruments as well for a small fee.
Best of luck

Well depending on your price range it varies. If your range is in the 3000 dollar ( American) range and up. I would suggest a Haynes,Pearl, or Altus. If you can go upwards of 5000 than any of those plus Powell, Muramatsu,Sankyo, or Burkart. Any of those would last you for a long time. Go to the closest music store that has a good selection and try as many flutes that meet your criteria as you can. Or if you can find someone you know who has a flute you'd be interested in, ask them if you can try their flute and see if you like the feel. Some companies will let you arrange a trial period of their instruments as well for a small fee.
Best of luck

<Added>

Also Never I mean ever! Buy from ebay, I'm not saying that ebay is completely bad, but for instruments I don't trust it. Also used flutes are perfectly fine, most of the time they're just as good quality as new for a lower price. And finally some other Quote, budget brands you may want to check out.
Sonare-Powell
Resona-Burkart
Azumi-Altus
Amadeus-Haynes
All of these come with a hand made headjoint on a lower quality but still very nice body and foot joint.

Thanks for the recommendations!
I forgot to mention though - I can't really spend more than 1000€. Pearl seems reasonable to me, are cheaper models also good?

Pearl is a very good brand. I would look into an azumi 2000, those are a little over a thousand. You can often find used quality intermediate flutes for around a 1000, so I would look into used for the best quality for the amount you can spend.

One thing to note is that the quality of the instrument has almost nothing to do with the metals used. A lot of makers make less expensive bodies with a professional headjoint added.

Brannen makes Avanti as their budget model
Altus makes Azumi
Powell makes Sonare
Haynes makes Amadeus
Pearl is their own company aimed at the middle-market.

Any of these five are good choices because you can save a lot of money and get quite a decent sound. One extra thing to note is that all modern concert flutes are tuned with a B footjoint in mind, so get that if you can.