Anyone considering this should read the ANO (UK) or equivalent document for their country.
There are two guides for the UK that summarise the relevant parts (emphasise that these are guides, ANO is always definitive):
https://www.caa.co.uk/default.aspx?pageid=8791
http://www.caa.co.uk/docs/33/Informa...ice2015029.pdf
The most pertinent section appears to be this:
5 How to determine whether or not a flight which is not commercial air transport is public transport
5.1 To determine whether or not a flight which is not commercial air transport is for the purpose of public transport of passengers, the first question is whether or not there are any passengers on board. This is not always entirely straightforward as an occupant may claim to be a member of the crew.
5.2 Having determined that there is at least one passenger on board, the next question is whether any payment has been given or promised which, if it had not been given or promised would mean that the passengers would not have been carried. If there is any payment which could fall into this category, consider what would have happened if the passenger had presented himself for carriage and announced that such a payment would not now be made. Would the passenger still be carried?
As long as you are confident that you would be able to satisfy any queries surrounding flights undertaken through this weflymate (or similar) website, then fill your boots.
SD