It's not so terrible if you are in Greece. I would not call a 500euro base salary expensive, that might even get you someone with postgraduate studies in the current conditions. On the law system I totally agree. Good for law related startups?
So even if seller and buyer are in Greece, freelancer.com (warning: don't use them) is in Australia. Receipts won't make it to the authorities. Also: freelancer.com won't care if you use a fake identity, as they're extremely scummy and in this case it works to your advantage.
Why is it an acid test of competence to you? For the theoretical knowledge they imply?
Because they are so basic. If you've never heard of a linked list, it means that you've got absolutely no education (formal or self-directed) in programming. (Even looking at the Java docs, you'd eventually notice the core LinkedList class.) If you've heard of a linked list but have no idea what it is, it means you've got a terrible education (if formal) or no curiosity (if self-directed). If you know what a linked list is but can't program one, it means you're incompetent.
I can't imagine the existence of a competent dev who can't write a linked list class/struct/whatever.
Even if you don't know how to implement them you at least need to know how they work and their performance characteristics. I would not expect them to be able to implement one in C but at least they should what the fuck it is.
This kind of 'orthodoxy' (you must know about X) confuses computer science (purely academic) with business outcomes (what engineers are paid to deliver).
I've never had to create a GPU, but if I didn't know what it was, I wouldn't be good at graphics development.