When a Liqudity pair is created via a DEX, an event is emitted.
Sniping bots are able to listen for this event (or any event from the DEX itself as long as they have the tokens smart contract address).
Once the bots are able to see that the event happened, they are then able to front-run all other trades making sure that they get in at the lowest possible price. They circumvent all normal means of trading (f.e. using a DEX's UI).
The inherent risk from participating in a public launch, especially one that is 'hyped' up is that everyone knows when a launch is generally going to happen and the people who operate said bots are going to be the ones who take advantage of that.
There are many anti-bot measures out there; however, skilled botters are always de-compiling smart contracts and adapting to what's going on in the space. It's a never ending fight between botters and legitimate traders. People are always looking to get ahead.
I would also give caution to projects that promise high returns on launch or boast about mechanics that inherently "print millionaires". If something seems to good to be true, it probably is. Especially in the cryptocurrency space...
Always do your own research. The main takeaway from this is that you should be aware of this possibility when participating in project launches.