So... Before you buy into it, get a financial statement and some financial history, and check whether the "wet" rate indeed does include all maintenance and reserves for replacement parts and such, and that these reserves are, at present, sufficient. (So if the engine is half-time, there should be 50% of the cost of a new engine in the engine fund.)
If you manage to get hold of the financial overview of the last three to five years, then you can easily see if the members were ever required to pay anything above and beyond the monthly and wet price, and see if this was because of bad planning, or because of unlucky circumstances.
And remember that planning your maintenance cost for a very common type (a PA-28, C-172 or something) is fairly easy since there are a lot of maintenance firms and lots of these shared planes around, so lots of experience with the actual maintenance cost of the type. But if you're buying into something unique, less people have experience with maintaining it over a long period, and it is harder to predict the costs of that maintenance.
But at the end of the day you've got to accept that you're owner (even if only part owner) of an aircraft and that you may be unlucky with the engine or whatever, requiring unplanned repairs that are not covered under warranty or insurance, and thus requiring additional funds. If you don't want to run that risk, go rent. (And this equally applies to cars, houses, caravans and other capital goods.)
And there's another tricky thing too. Everybody is interested in low flying cost. So a share in a plane with a 60 euro wet rate will sell more quickly than a share in an identical plane with a 70 euro wet rate. That's because the only thing mentioned in the small ad in the magazine is the monthly fee and the wet rate. Not the present state of the engine fund (if any). So from a marketing point of view it is a good idea to lower the published wet rate, while the members of the group know that they're going to have to put up more money at some point in time to pay for repairs. Not a problem as long as this is out in the open, and you know what you're getting into.
Me, I would get the financial data and prefer buying into the group which seems to have its finances in order, with the wet rate covering all the expected maintenance plus a bit of reserve, both for the 3-5 years past and 3-5 years to come, than buying into the group with the lowest "wet" rate.