Rating Methodology
How we calculate installer ratings on Why Solar, and why we built the system this way.
Why a Trust Score?
Star ratings from customer reviews are valuable, but they tell an incomplete story. An installer with two five-star reviews could be excellent or could simply be new. An installer with hundreds of reviews and a 4.2 average has a far more reliable track record.
The Why Solar Trust Score fills this gap. It assesses installers on publicly verifiable criteria like licensing, insurance, and business longevity, then blends with customer reviews to produce a single composite rating that becomes more accurate as more evidence accumulates.
The 10 Trust Score Criteria
Each installer is scored 1 to 5 on ten criteria. These are not weighted equally. Safety-critical signals like licensing and insurance carry more weight than proxy signals like company size.
| Criterion | Weight | What it measures |
|---|---|---|
| Verification of licences | 20% | SAA and CEC accreditation status |
| Insurance coverage | 15% | Whether the installer holds public liability insurance |
| Consumer review quality | 12% | Average star rating from verified customer reviews |
| Consumer reviews volume | 10% | Total number of published reviews |
| Time in business | 10% | Years the company has been operating |
| Network verified | 8% | Whether the installer has been vetted by our network team |
| Transparency of credentials | 8% | Willingness to disclose accreditation numbers, insurance details |
| Range of services | 7% | Breadth of offerings (solar, battery, heat pump, EV, commercial) |
| Company size | 5% | Team size as a proxy for operational capacity |
| Service area coverage | 5% | Number of states and territories served |
The weighted average of these scores produces the Trust Score, displayed on a 1 to 5 scale with tier labels: Elite (4+), Strong (3+), Good (2+), or New.
Bayesian Review Average
Raw review averages can be misleading. A single five-star review does not mean an installer is perfect. To address this, we use a Bayesian average that starts every installer at 3.5 stars with five "virtual" reviews. As real reviews accumulate, they gradually pull the average toward the true rating.
We also apply recency weighting so that recent experience matters more:
- Reviews from the past 12 months count at full weight
- Reviews from 13 to 24 months ago count at 66%
- Reviews older than 24 months count at 33%
Composite Rating
The rating displayed on each installer profile is a composite that blends the Trust Score with the Bayesian review average. The Trust Score acts as an anchor (counting as five virtual reviews), and customer reviews gradually take over as more are submitted.
The formula: (5 × trustScore + reviewCount × bayesianAvg) / (5 + reviewCount)
For an installer with no reviews, the composite rating equals their Trust Score. With 5 reviews, customer feedback accounts for roughly half the rating. With 20+ reviews, customer sentiment dominates.
Disqualification Rules
In serious cases, such as ACCC enforcement action, CEC accreditation suspension, or insolvency, we may flag an installer as disqualified. When this happens:
- The Trust Score tier badge is replaced with a warning notice
- The composite rating is capped at 1.0 regardless of reviews
- The profile page explains the reason for the restriction
Disqualification is an editorial decision, not an automated rule. It is reserved for cases where continuing to display a normal rating would mislead consumers.
The "Auto" Label
The Trust Score section displays an "Auto" badge to indicate that the score is calculated automatically from publicly available data. No installer can pay to improve their Trust Score.
We reserve the right to make editorial adjustments in exceptional circumstances (for example, if data sources are temporarily inaccurate). Any such adjustments are disclosed on the installer profile.
Questions?
If you are an installer and believe your Trust Score contains an error, or if you are a consumer with questions about how ratings work, please contact us.