Ours was a summer of not very good experiences. We decided that sharing our place with others is not for us and having others helping with our work is also not for us - they never do it our way

We are obviously not a very gregarious pair
Some of the things we learnt are:
# always supervise - don't leave your workers to carry on on their own. They will not value your tools and property and a small mistake can and will turn into something expensive if you're not around.
# any job will take longer with a HelpXer there so you need to be realistic about what can be achieved during their stay. We spent longer undoing their mistakes than we got benefit from their help, and we spent more on food than could be justified by the work they did.
HelpX works well if you have heavy jobs or jobs which need an extra pair of hands. If that's what you want them for then have the jobs ready before they get there, so you get maximum benefit from their help.
Find out in advance if they have a particular skill which you want to use, and have it set up to start work as soon as they arrive.
# research your helpers thoroughly before they come. If you have children then be EXTRA careful about who comes to stay - this sort of scheme is an excellent hunting ground and very difficult for the organisers to police.
# set a short stay initially - say a week or a fortnight - it's awful if you don't get on and they will be staying for a couple of months.
# lay out their work hours before they arrive - about 4 or 5 hours a day is about normal
# we had expected ours to go out to explore in their time off but none of them would budge, so while we were still working to all hours, they were loafing around waiting for me to cook their dinner.
# they eat loads !
# we had ours one by one - I'm not sure if a couple would be better or not.
# don't take any crap.
# if possible, don't have them living in your house unless you really don't want any privacy or free time for their entire stay. Ours stayed in our granny flat and I think it was just too comfortable for them so they didn't want to go out or leave. Bunkhouse style accommodation or a caravan would be better if you have it.
# on the plus side, you meet interesting folk from all over the world and have some amazingly good conversations.
# get your Health and Safety equipment in place before they arrive and don't expect them to do anything remotely risky, because they won't.
# assume they don't know a weed from a crop.
# don't get too friendly or they'll get bossy

and won't leave
In the end we decided having HelpXers was more stress than it was worth, but our situation is unusual so it was bound to be difficult to fit strangers in.
We know of people who work their holdings almost entirely with HelpX and Woofs labour and couldn't manage without it.