In בבא קמא נח ע' ב the gemara doesn't want to learn two דינים from the same verse, while in many other gemaras (סוטה כט ע' א) the gemara has no such problem.
When does the gemara learn two stuff from the same verse and when not?
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In general, this will be addressed by the commentaries to the talmud. A very useful resource is the sefer Torah Temimah which deals with the Talmudic interpretations on a verse by verse basis. Nevertheless, I will try to give a few general rules as to when one might learn two halachos from one passuk.
The basic idea is that one could only learn the minimum from any specific drasha. So for example, if the Torah says a rule that requires a multiple of something, that means two, which is the minimum of multiple numbers. Similarly, if a word or letter is extra, one can only make one drasha to explain the extra word. Sometimes, however, there are more than one extra words or letters in a passuk, which require multiple drashos. (Many disputes in the Talmud revolve around whether a word or letter is extra or not, see Megillah 2a for example.)
A good example is the case the questioner mentioned in his comments. The first halacha comes from a grammatical reading of the word השב (Rambam there), and the second comes from the extra word תשיבם. (h/t Torah Temimah, which is my go-to sefer for these issues.)
3.Sometimes the Gemara will make an asmachta or attribute a law to a verse even though the law is not actually derived from the verse. In that case, the law might be attributed to a verse that really teaches a different halacha.