Rule #1: don't trust automated tools... ever
Rule #2: always think hard about the potential end users (buyers), how these domains could be used for a business in the real world. A good domain is a domain that you should be proud to advertize, put on your business cards etc. A good domain normally speaks for itself, should be commercially viable and have a clear purpose.
Rule #3: your domains must be great, not just 'ok' domains. If I can find an available domain of similar or superior quality that will do the job just fine - then why should I buy your domains in particular ?