Parisgoing, again, when suggesting anything to do with work it is important to add the caveat, 'If you can legally work in that country.' Helpx, workaway, WWOOF, et al exists in many countries where someone who is there as a tourist (no work permit/visa) cannot legally participate. That an organization exists in a country does not automatically mean you can participate.
For example, it is illegal for a tourist to participate in any such organizations in the US, the UK, Spain, to name a few. On the other hand it is legal for a tourist to participate in Canada for up to 30 days. You have to check the law for each country you are considering doing it in.
If you then choose to participate illegally, that's your business but if you know whether it is illegal or not, you can weigh the potential consequences against the gain and made an informed decision, not get a rude awakening as this girl did.
http://www.cbc.ca/news/canada/ottawa/story/2010/05/12/gatineau-vroemen-border-windsor.html