The catch-phrase "junk science" has been popularized to describe situations in which the testifying expert, and/or the expert's testimony and conclusions, are considered or found questionable because of an allegedly poor or insufficient scientific foundation.

The testifying expert should be aware that cross-examiners may pursue some of the following lines of questioning in an attempt to address a supposedly inadequate, incompetent or unprofessional forensic witness:

• The cross-examiner may try to show that the witness is not knowledgeable on the subject.
• The cross-examiner may try to expose a lack of meticulous attention to detail that the expert witness failed to follow in preparation.
• The cross-examiner may try to show the expert witness as having a lack of activity in the professional field, particularly with regard to absence of current education and training, and lack of appropriate seminar and workshop attendance.
• Whenever possible, the cross-examining attorney should avoid allowing their expert to recognize the "charlatan" as an expert. Establishing that the witness has never testified to the same effect previously can be damning cross-examination.
• If the cross-examiner can establish that the findings of the witness are not consistent with studies of others, credibility of the testifying witness may be eroded.
• If cross-examination can suggest that findings of the expert often lead to erroneous results, the expert's credibility may be jeopardized.
• Often an expert will indicate that present methods are positively related to prior methodology. If that linkage and connection can be dispelled, the weight of testimony and credibility of the witness can be threatened.
• The witness should be pressed for literature that tends to support the testimony.
• Absence of such literature bolsters the claim of lack of competence and credibility.
• If tests or examinations conducted by the forensic expert have never been admitted as evidence in a court or other dispute resolution process on previous occasions, such lack of admission seriously questions the validity of the extant testimony.
• Expert witnesses who use animal tests to support their conclusions can be cross-examined by establishing the differentiations between animal testing, animal subjects, human subjects and human results.
• The aggressive cross-examiner will often show that there is no government regulation or statutory support for the expert testimony or that the expert testimony is simply not approved either by the scientific community or by any government-sponsored methodology.
• If the cross-examining attorney can establish that the scientific, technical or professional community does not rely on the same tests, procedures or techniques followed by the expert, a serious erosion of the expert witness's testimony may occur.

There are specific steps the expert can take to be more prepared and less vulnerable to cross-examination:

1. The expert's résumé must accurately reflect verifiable accomplishments. The expert should not exceed the bounds of personal expertise.
2.   In accepting assignments and answering questions, the expert should not venture beyond areas of professional qualification and proficiency. The temptation is great to move into areas in which the expert is not qualified, but image and credibility are enhanced by sticking to the expert's field of knowledge, training and experience.
3. The expert's preparation must be complete. Whatever investigative steps have been taken must be completed and fully documented. Thorough preparation to testify will be exemplified on direct examination. Accurate investigation creates a dense fabric of fact that becomes difficult to penetrate on cross-examination.
4. The expert should make direct examination persuasive. If the expert is believable and has done all of the homework, persuasive abilities will be obvious. Psychological persuasion conveyed by body language, repetition of theme, and appropriate dress and demeanor all add to a positive impression.
5. The smooth, solid presentation the expert makes on direct examination must be maintained throughout cross-examination. When the examiner asks a potentially damaging question, the expert should use the same air of certainty displayed on direct examination. The expert may say, "Yes, that is correct, but let me explain." This does two things: First, the expert has signaled the sponsoring attorney to come back and ask for an explanation on redirect. Second, the expert has displayed credibility in a forthright, unapologetic manner.
6. The witness who is certain of the technical effort and preparation is questioned more cautiously on cross-examination. The cross-examining attorney quickly senses the expert's truthful and positive answers.
7. The expert exercises an ability to teach. Part of the stimulation of a classroom setting is the ability to field questions from students. The skill with which those questions are responded to is often the mark of a great teacher. The expert's function as a teacher is an extension of that exercise. The cross-examiner who probes the expert's qualifications, preparation, conclusions and opinions will press for answers.
8. The expert must be familiar with previous writings and testimony. The expert may have written articles, books or reports during a professional career. The forensic analyst may have testified in depositions or at trial on prior occasions. The expert's personal library should include reprints of every authored article ever published, and every deposition and court transcript. The testifying expert should know his complete bibliography and transcripts, which are all potentially accessible to a diligent opposing counsel.
9. Opposing counsel seeks to find prior statements, in either the expert's writings or testimony, that contradict the opinions tendered in the current case and use them in cross-examination. The expert may be asked to produce some of those inconsistent statements during the discovery phase.
10. The proffering attorney will need to know about the expert's prior opinions. Therefore, the expert should index all prior writings and testimony. These can supply positive support or rebuttal material for cross-examination as well as alerting counsel to vulnerable areas of cross-examination.
11. If the expert has written or testified contrary to the position now taken in the current case, awareness of the potential conflict is important. The basic premise that supported the testimony in the former case may be different from that of the current matter.

Understanding the rationale and principles upon which prior writings or testimony were based, and distinguishing those of the current case, can minimize the effects of cross-examination and, in some situations, solidify the expert's direct testimony.

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