Community colleges are increasingly recognized as providing an accessible and affordable pathway to STEM occupations, particularly for underrepresented racial and ethnic, first-generation, and low-income students. There are several institutional and academic factors that influence transfer outcomes. But one of the most central factors that can either help students successfully navigate the two-to-four-year pathway or cause significant roadblocks and cost students considerable delays -- is advising. In this study, we investigate how advising practices at three institutions -- two community colleges and one university -- contribute to the success of underrepresented students on the transfer pathway in STEM disciplines. We conducted interviews with 39 near-transfer or recently transferred students in STEM. Most students experienced at least some good advising (n = 28); however, 21 students reported poor advising experiences, which in some cases created undue challenges and barriers. Positive advising experiences contributed to students' sense of trust with their advisors, departments, and the institution. Early positive relationships with advisors also contributed to students being more likely to seek future help from advisors (including at other institutions); conversely negative advising relationships contributed to students being more likely to seek help elsewhere, like from friends or family, and sometimes giving up and not receiving any help at all.