Although I am usually middle of the pack for efficacy of 3-D paste inspection, it is critical when applying conductive epoxies.  The criteria that I am aware of or have utilized are as follows:
IPC-3406
IPC-3407

Before assessing visual criteria, I must first re-affirm Yuan-chia Joyce Koo's position that HALT is essential to process verification.
Normal prohibitions aside (do not use on a HAL (Hot-Air Lead-Free) or HASL (Hot-Air Solder (Tin-Lead) Level)), then the ideal is to make sure that the parts are not mashed into the epoxy.  The best results I have achieved are with the epoxy compressed roughly 1/4 to 1/3, with 2/3 to 3/4 of the epoxy bond under the part terminations

Also, make sure your stencil house has epoxy experience as they will fabricate the stencil to different guidelines.

Also, two past resources for me were Zymet and Parker Chomerics.  I have used conductive epoxies from both and they were helpful.  Master bond also offers conductive epoxies but I cannot vouch for their tech support.