And by what metric do you separate the competent experts from the non-competent experts?
There’s no hard-and-fast rule, obviously, just as there’s no hard-and-fast rule for figuring out which meta-analyses you can trust (for problems with meta-analyses, see e.g. [1, 2, 3, 4]). But if the experts explicitly discuss the reasons behind their opinions and e.g. why they think that one particular meta-analysis is decent but another one is flawed, you can try try to evaluate how reasonable their claims sound.
There’s no hard-and-fast rule, obviously, just as there’s no hard-and-fast rule for figuring out which meta-analyses you can trust (for problems with meta-analyses, see e.g. [1, 2, 3, 4]). But if the experts explicitly discuss the reasons behind their opinions and e.g. why they think that one particular meta-analysis is decent but another one is flawed, you can try try to evaluate how reasonable their claims sound.