Our answer to this depends on which test you took.
The PTE results are generally very reliable - Pearson already scores every test twice to be safe! Added to that, technical issues, such as faulty microphones, are very rare. Even human error like loud breathing is much more common and is not considered a technical issue.
Most importantly though is that due to the computerised nature of PTE, marks can be revised down as well as up, and a score decrease is actually more likely than a score increase.
Hence, for PTE we recommend that it's always best to prepare for the exam and sit the exam again rather than a rescore.
For more thoughts, see our blog post on the topic!
The marking for the Listening and Reading sections is computerised, thus is unlikely to change much. On the other hand, the marking for the Writing and Speaking sections is done by human examiners who can be subjective, and so your score may well change - either up or down!
We usually only recommend a rescore if your Writing or Speaking score is already reasonably high AND you are confident that it could be increased a bit further.
You can read about the OET re-marking policy here.
You can read about the IELTS re-marking policy here.
Note on Requesting for an IELTS Re-mark
Each test centre may have a different re-mark application procedure. For example, this is the procedure of applying for re-marking with IDP Australia. We recommend that you contact your IELTS test centre to find out about your Enquiry on Results application.