I have seen the words 売春 and 買春 pronounced "ばいしゅん". From my understanding 売春 is taken from the perspective of the "seller" whereas 買春 is taken from the perspective of the "buyer". However, when I pronounced the later as "ばいしゅん" in front of a native, I was told that it is pronounced "かいしゅん" (買春). Is this reading valid and does it carry a different context when pronounced this way than the former reading?
Short answer: Both readings have the same meaning. Whether you consider かいしゅん as a valid reading of 買春 or not depends on what you count as “valid.”
Some Sino-Japanese words have not only an on reading which is shown in dictionaries as the primary reading but also an alternative reading which avoids ambiguity with some other words. 買春 is such a word. According to dictionaries (Daijirin, Daijisen), 買春 is primarily read as ばいしゅん, but it is often read as かいしゅん to avoid possible confusion with 売春 because the context is not always enough to distinguish 買春 and 売春. Here かい comes from the kun reading of kanji 買. Whether it is read as ばいしゅん or かいしゅん, the meaning of the word 買春 does not change.
Daijisen lists かいしゅん as an alternative reading of 買春. Daijirin does not. (I suspect either the word 買春 itself is new or it became common recently, and that the need for the alternative reading arose recently; but I do not have any source to back up this speculation.)
Other examples of alternative readings like this are 市立 and 私立. The primary readings of both words are しりつ, but particularly when talking about schools, しりつがっこう can mean both 市立学校 (school operated by a city) and 私立学校 (school operated privately), and this is extremely confusing. Therefore, 市立 is often read as いちりつ and 私立 is often read as わたくしりつ.
Returning to your question, whether かいしゅん is a valid reading of 買春 or not depends on how you define the word “valid.” It is common, and there is a reason for this reading. My personal impression is that reading the word 買春 as かいしゅん is much more common than reading it as ばいしゅん; at least, I have never heard 買春 read as ばいしゅん. I think that these are the reasons why you were told that it is read as かいしゅん. However, not every dictionary lists it as a reading of 買春.