Although the dictionary states that both the plural and singular verb forms are correct, logically, I would like to emphasize that native speakers tend to utilize the determinate number "pair" in this context: a pair of scissors, which would require the third person singular verb form.
I guess that since "scissors" actually means "cutters" from Latin, if you took a pair of scissors apart, then you would have just a cutter, which would be a countable noun.
Hence, I would use the plural verb form, but might just be from the discourse I find myself surrounded by. Another native speaker in a different culture might employ the singular verb form, however unlikely.
Eric Paul Monroe