Well, the guarantee has a lot to do with the team and as long as the team is fake, have no idea of what they are doing and have no mindset of working on a product, things like this will always happen.
Practically, with all I have said above, it is now left for every individual investor to try as much as possible to read a whole lot about the team and try to verify their authenticity and it is a good thing we have the likes of ICObench where KYC is done for the team, and knowing that this is a team that can deliver based on their profile, you will somewhat be rest assured that you can at least trust them not to scam you.
Secondly, product is one very important thing to look out for, its availability, the prospect in the long term and your belief in it. These two things can save you a whole lot of pain losing your money in the end.