Not sure what you are getting at. Until you're on the localiser, trusting or not trusting the glideslope is irrelevant.
Unless you're talking about CDA. In which case, I find that it depends on the aircraft. On the 737NG I found that the G/S indication was pretty reliable on an intercept angle. But on the A320 the indication seems to fluctuate up and down considerably so I use the projected level off arrow to judge what V/S I need to avoid levelling off before the G/S.
P