If a conflict of interest is not literally declared, is it safe to assume there is a conflict of interest? What does this imply about the findings?
Conflicts of interest on their own do not imply poor results is the blanket answer to this question.  It is true that in several high-profile (and most likely lower profile) research projects funded by industry that muzzling or cherry picking has happened (here is an interesting analysis of one particular industry and its issues).  Industry obviously has an interest in funding research that will give them favorable results.  However, just because industry has funded the research does not mean that it is automatically untrustworthy.
Unless there is good reason not to, we have to trust in the peer review process and acknowledge that it is our job as readers of research to interpret and contextualize studies regardless of conflicts of interest.   For instance, we should always be sure to thoroughly read and understand the methods used in the research and to determine if they are up to acceptable scientific standards.
It is similarly important to understand that a single study or suite of studies does not imply scientific truth.  For instance, if a paper shows that they were able to observe a particular thing in a particular population, that implies only that the observation is possible under certain conditions, not that it is universal.
Conflicts of interest are also sometimes unavoidable.  A drug company trying to do trials of a specific, proprietary drug must fund those trials.  That's a conflict and they obviously have an interest in favorable results, but just because that interest exists does not automatically imply that the results will be untrustworthy.
Finally, just because something is not declared does not mean that you should automatically reject it.  Of course be critical, but don't assume that just because something is unclear the authors are being evasive.  At the end of the day you can always try to send an email to the corresponding author and ask.  Worst thing that happens is you are ignored.