If you're looking to run Capterra/G2 ads go through this process:
1. Do they have the right category for what you sell? If it's not the right category, the quality of leads will probably be bad.
2. If they do, check how many reviews your competitors have compared to you. It's always a worth getting more reviews on these sites.
3. Once you have competitive number of reviews (and optimise your profile), you should start seeing organic traffic from them.
4. Check how the organic traffic is converting. Also check their native analytics.
5. If the organic traffic is converting well, it's most probably a good idea to pay for that traffic. ,But you'll still have to see what the CAC is in your case.
Things I've noticed:
1. Click to landing page view ratio is much worse than Google ads. (Use pageviews not clicks when getting a sense of CPCs and CRs)
2. It sometimes has given as as good results as Google ads.
3. If unit economics are working REALLY well for you and there is a high profile visit volume, it may be worth checking out G2s paid audience.
4. In one case we saw 2x CPCs than Google but also 2x CRs with similar lead quality. So the cost was pretty similar to Google.
5. In another case, where the category was just a little off, we only got junk leads.