(This section is for beginners in the hobby of collecting WW2 German medals)
Starting your own collection of medals is a alluring thought for many. You may consider two main options:
1. Collecting reproductions of medals (and hopefully paper collateral) for display, reenacting, etc
2. Collecting originals
Option 1 is much simpler by being practically risk-free and much cheaper. Disadvantage is that your collection won't really be an investment that has a chance to increase its value over time. There are various quality of reproductions too. Paying extra $5 or $10 may buy you much nicer one. Look for details. German medals were made mostly by jewelry companies. They were beautiful, precise and elaborate. Especially early in the war.
Option 2 is a perilous path and requires much more time (to find stuff, learn, etc) and money. There are many good looking fakes out there sold as originals and unless you do due diligence, join forums, verify with experts, read books on the subject you may easily buy junk for lots of money. As there are many items you could collect, knowledge necessary to tell fakes from real is vast. This will likely only get more difficult over time as forgers gain knowledge of better techniques to do their dishonest job. The advantages of collecting originals on top of the feeling of owning a piece of history is that long term they are likely to increase in value. Of course unless civilization as we know it collapses, or fakes become indistinguishable.
Places to avoid at all costs:
ioffer.com - total disaster. I think I've never seen anything authentic there. Good for reproductions though if sold as such
ebay.com - no-nazi policy makes it rare, but many things there are fakes sold as originals
craigslist.org - full of fake aged replicas
Places to go to:
Specialized auction houses (google for "militaria collection auction house"). These sometimes sell fakes too, though.
Facebook groups of collectors (e.g. "ONLY German WWII Items Sale, Buy, Trade, Questions, and Forum" or "WWI & WWII Quick Sell 48-Hour Auction" - thousands of experts there make sure fakes are called out if they show up.
There are many online stores which sell more expensively than the sources above and some of them mix authentic medals with fakes. Quite risky for non-expert. There is also dedicated Facebook group "Identifying German WWII FAKE Medals & Badges" where you can submit questions and some domain expert will surely help you.