Very flimsy.
There appears to be multiple trees in my heritage with the same forenames for parents and siblings, even spouses, but the mother's maiden surname is different. Dates of birth/death and places of birth death differ also. I am reluctant to merge any of these trees as it's most likely that a lot of these details have been plucked from FamilySearch records and assigned incorrectly and each person in these trees may in fact have wrong details and have all been mixed up.
I've just looked at one tree with a Louisa Abraham's as a sister and the amount of matching with differing details but with similar familiar fornames is overwhelming to deduce if this Sarah's tree is actuality correct based up the alleged siblings, parents or spouse.