It is known that Verwey transition can be drastically modified by the stoichiometry. So there is no wonder that unless someone is very careful about preparation and stoichiometry he will get inconsistent results. Now coming to nanoparticles we know well that most of the nice transitions that have been observed in bulk disappears in nonosamples. I am sure Verwey transition will disappear in small enough Fe3O4 particle, because Virwey transition is the emergent phenomenon of a N-body system where N is large. There can be no superconductivity for a single atom because superconductivity is also an emergent phenomenon of a collection of large number of particles. So what you need is to study Verwey transition of stoichiometric Fe3O4 samples of diminishing size. When you make the paricle size small enough the Vewey transition must disappear. But if your preperation does not give stoichiometric Fe3O4 nanoparticles then you may observe disappearance of Verwey transition even for larger particles and unless you are careful you may conclude wrong things. If you characterize Verwey transition by resistivity measurements you have to be very careful about the contacts. You may consult the following thesis available in the web:

Investigation of Electrically Driven Transition in Magnetite, Fe3O4, Nanostructures

by Alexandra Fursina, Rice University (2010)

Both size effect and shoichiometric.

I have also some doubt about the verwey transition in magnetite. we cant observe the verwey transition in nano Fe3O4. But some reports are available that, octahedral shape nanocrystals show the verwey transition and spherical one not exhibit that. Are all the Fe3O4 samples have low-temperature monoclinic phase, even though it is not visible in nano Fe3O4? ie., Are all Fe3O4 have a transition near 120K, even though it is not visible in M-T measurement?