[Solved] 1-wire DS18B20 sensors keep dropping
I wouldn't trust any pre-made waterproof cables to have authentic DS18B20 sensors unless you can verify with the supplier that they received their sensors from Maxim or a reputable dealer that did (e.g. Mouser, Digikey), but even that's not a guarantee. I'd at least verify I could return the sensor if it's found to be counterfeit.
I've always waterproofed my own. Solder it to wires, then dip or spray plastidip, or coat in epoxy. I've had several going strong for years in fully submerged and high humidity environments.