I didn’t realise it was possible to trigger review invites on the free plan with TrustPilot, but I’m told they allow 100 per month to be sent. This then becomes a CC to a dedicated TrustPilot address linked to your account on order fulfillment.
I suppose we could link it to the payment notification email, but I’m not sure that would work for all users? I’ll give it some thought and let you know if I have any ideas.
We bounce between 4.7 and 4.8 on TrustPilot, the category we’re more focussed on is “Accounting Software”. You’re right though, they don’t tend to weigh the ranking by total review count. It’s not too difficult to get a very high ranking with under 100 reviews.