1. Price: Service that is too cheap may not be credible. If a service promises that you can publish SCI papers at a very low price, it may be a signal that their service may have problems.
2. Transparency: A credible service should be transparent to its service process and price. If they don't tell you their workflow or are vague about your question, it may be a signal that there may be something wrong with their service.
3. Evaluation: It is also a good way to check the evaluation of other customers. If you can't find their comments online, or all the comments you find are negative, then this may be a signal that there may be something wrong with their service.
4. Contract: If a service requires you to pay all the fees first, it may be a signal that there may be something wrong with their service. Good service should be charged after you accept their service.
5. Legitimacy: Finally, you need to ensure that their services are legal. If you have any questions about their legality, you can consult a lawyer or relevant government departments.
Generally speaking, publishing SCI papers is a complicated task, which requires you to have profound research skills, good language skills, enough patience and perseverance. If your ability is limited, you may need to seek professional help. However, you also need to pay attention to prevent being cheated.