I think scoring is subjective.

1. Usually, we give score 1 if answer of particular question in the checklist is YES, and 0 for NO.

2. Then sum all scores

3. Categories included studies based on some cut-off score, such top scorers high quality, then medium, and low quality

https://jbi.global/critical-appraisal-tools.

The scoring has to be orderly and consistent. Cut-offs can be made on that basis

I suggest checking the STROBE Checklist checklist: cohort, case-control and cross-sectional (combined) studies at https://www.strobe-statement.org/ can help you with a verification roadmap

STROBE represents an international, collaborative initiative of epidemiologists, methodologists, statisticians, researchers and journal editors involved in the conduct and dissemination of observational studies, with the common goal of strengthening the reporting of observational studies in epidemiology.

How do you calculate the 'unclear' section?

After sum all scores

Categories included studies based on some cut-off score, such top scorers high quality, then medium, and low quality according to Mathematical Logic.

The authors often receive queries from reviewers wishing to use the tool to provide advice on how much weight to assign each question, and what the cut-off score should be for inclusion in a systematic review. These questions presuppose that the purpose of appraisal in systematic reviews is to include only those studies that are of high quality and to exclude those of poor quality. While this is one way to use the results of critical appraisal in reviews, it is not the only approach, and it may not be appropriate in many situations. The guidance to authors wishing to use this tool in terms of cut-off values/scores and determining whether a study is low, moderate or high quality, is that these thresholds are best decided by the systematic reviewers themselves. Generally, cut-off scores are advised against, because the critical appraisal questions are not all ‘‘equal.’’ As such simply tallying the ‘‘yes’’ responses does not truly give an accurate indication of the specific problems of a study. The authors suggest presenting the results of critical appraisal for all questions via a table rather than summarizing with a score. Ideally, two reviewers will be involved in the critical appraisal for the review

Munn Z, Barker TH, Moola S, Tufanaru C, Stern C, McArthur A, Stephenson M, Aromataris E. Methodological quality of case series studies: an introduction to the JBI critical appraisal tool. JBI Evid Synth. 2020 Oct;18(10):2127-2133. doi: 10.11124/JBISRIR-D-19-00099. PMID: 33038125.

Thank you for this answer. Very helpful.