Short answer: yes, as long as you buy smart. Here is how to do exactly that.
The short answer
Buying game keys online is safe when you use a reputable store and pay sensibly. The vast majority of purchases go through without a hitch. The trick is knowing how to pick a good seller and spot the rare bad one before you pay.
Buy from stores with a track record
This is the big one. Every store on XD.deals carries a rating from real buyers, so you can see how it has handled other people before you trust it with your money. A shop with thousands of good reviews is a very different thing from one nobody has heard of.
Pay with a method that protects you
Use a payment method that comes with its own buyer protection, like PayPal or a card. If a purchase ever goes wrong, that protection is your safety net and makes getting your money back far easier.
Check the region before you buy
A key locked to another region is the most common reason activation fails, and it is completely avoidable. Read the region line on the listing, and when in doubt go for a Global key. Our region-locked keys guide has the details.
What to do if a key does not work
First, retype it by hand in case a stray space slipped in from copy-paste. If it still fails, contact the store you bought from, because a shop with buyer protection will sort it out. You can also write to us and we will help you figure out what went wrong.
Our take
We would not run a comparison site for stores we would not use ourselves. Buy from a well-rated seller, pay with protection and check the region, and buying keys is every bit as safe as buying anywhere else, just cheaper.