Very low ball offers, the more shady ones will inspect your property and make up shit that is wrong with it and devalue it. They can then claim and sue you for not disclosing these "known problems" if you sell to another party later. To protect yourself you can get the home appraised prior to inviting one of them in and have evidence of their fraud (and can press charges) if they go that route, since you will have a licensed appraisal report.