Workaway is definitely not a scam outfit. I've been a member for 3 years now without difficulty. For those who say the hosts do not respond, well, as a host myself, I'd like to say that 60% or more of the volunteers who I may contact do not even have the manners to reply - not even with a 'Thanks but no thanks' response so it it isn't all one-sided although perhaps it may appear that way to anyone who is just enrolling!
In Europe it is highly unlikely that accommodation and food money is expected of you but in poor countries, they do tend to think that these 'wealthy foreigners' who can afford to travel can afford to contibute towards their keep.
I'd just like to add that communication beforehand is the way to a pleasant exchange - ask questions of what exactly would be expected of you and what the host expects in return. Check it out well beforehand to avoid unpleasant surprises.
That's life, as in anything some you win, some you lose!