I'm going to Germany for 3 weeks in December. While I'm there I'd like to order a few things off Amazon.de and have them delivered at the place I'm staying in (it's a paid apartment and the owners are not around). Can I sign up in Amazon.de and set the shipping address to the place I'm living in? Will I be able to receive packages etc.?
Last time I was in this situation I was careful enough to include the name of the house owner to the destination address (that's what c/o is for), so that the postman knows where to ring/in whose post box to place the package. Something like this will work:
John Doe c/o Addams Family 0001 Cemetery Lane Chicago, US
For completeness sake, the equivalent of c/o in German is p.Adr. which would result in:
John Doe p.Adr. Addams Family 0001 Cemetery Lane Berlin, Germany
It is not exactly clear why it's on travel but just write your name and the address on it, it's not like the postman is going to run a check against the land registry to see whether the package is addressed to the owners and refuse to deliver if not. When I was in Germany in a similar situation in 2007 I had zero problems receiving packages, including a laptop mailed from Japan. Can't imagine the situation changing materially since.
However, if you are worried then Germany has a ton of pickup locations, check About Pickup Locations for Amazon Deliveries for more.
As Aleksandr mentioned, the first step is to convince Amazon to try and ship to a new address. When I tried things like that, the Amazon site asked additional verification questions before they shipped it.
Amazon will then give the parcel to DHL. There are some reports how DHL subcontractors are under extreme time pressure and will not spend much time to resolve problems if nobody answers the bell or if they can't find your name on the door. If they can't deliver the parcel, it goes to a Deutsche Post office and the recipient gets notified. (If they find the address but nobody answers the bell, they might give the parcel to a neighbour and put a note into the mailbox.)
In the post office, you will have to identify yourself before they hand the parcel over. There could be a hitch if you can't show that you're living at the address, or if they haven't seen that kind of ID before.
The suggestion of a c/o address sounds sensible, but I haven't tried it.
A solution to several of the problems raised in the other answers might be to contact your hosts and arrange with them that you can order the item to arrive before you do, (if they live there and are willing to accept it for you or at their home address where they can arrange for it being delivered or collected.) I am sure many hosts will do, maybe at a small charge.
If the online seller is giving you a hard time, your host might even do the actual ordering but in that case you may have to send them the money before they order, that requires more trust than just accepting a package.
If you want to use amazon.de for ordering goods, one option is to not use your address at all and to have your goods delivered to a Hermes Paketshop. During checkout, the Amazon website will allow you to select one and shows its opening times. If you select this option, you will receive an e-mail when your delivery is at the Paketshop and then you can collect it from there during its opening times.
In many major cities, there are gas stations with pretty good opening times (e.g., 6:00-22:00) available as Paketshops. You need some form of ID (e.g., passport) to collect your items.
The advantage of taking this route is that you don't risk your package being delivered to the neighbour in case you are absent when the postman comes. Depending on the neighbours, the packet can be tricky to collect, especially if you don't speak German. Alternatively, the package can be taken to the next post office, which may have inconvenient opening times (some close at noon-ish on Saturdays, for example). Also, the Hermes Packshop has the advantage over the DHL Packstation that you don't need to register in advance (and thus do not have to wait for a couple of weeks for your Packstation card to arrive).
Amazon has unified accounts for their sites in various countries many years ago. If you have an Amazon.com account then you can use Amazon.de with the same account (not sure if you still have to do a registration step the first time you use it). You can specify an arbitrary delivery address. If you want to test that, you can buy me a gift :)
The real concern is avoiding tripping fraud prevention mechanisms. Given the amount of hacking that is going on lately, many organizations are on a hair trigger. Warning flags for them are shipping address being different from billing, credit card being used for online purchases in a different country, brand new online account created, package being sent to a hotel, etc.
I've noticed Amazon in general is fairly lax about fraud prevention, and you should continue using your account on amazon.de instead of registering a new one. You should notify your bank, but often the problem is not with them (since the store and its credit card processor carries the cost of fraud as well). So, your luck will depend on the store you order from. Shopping in a physical store has higher chances of success.