Is there a difference between the pronunciation of 개 (dog) versus 게 (crab)? Or do you just have to use context to know which one is being spoken about?
In theory (the "Standard" Korean language), there's a difference. In practice, there isn't.
On the other hand, if there's no context (e.g., "개/게 먹으러 갈까?", where both interpretation would make sense), since people "know" that they should sound different, they may exaggerate the difference to disambiguate. Then the vowel in 개 would move closer to ㅏ (somewhat similar to American English "cat"), and the vowel in 게 would move closer to ㅣ with more flattened lips.
Or they could just "spell it out": "아이" (ㅐ) or "어이" (ㅔ).
So if you can't hear the difference in a casual conversation, don't worry: it's perfectly normal.