I buy plants from fellow gardeners and I'm concerned that this is a Lysimachia vulgaris (loosestrife.) What do you think?
That is what it looks like
Growth habit and flowering looks more like Lysimachia punctata. Considered by many to be a desirable garden plant but can be an aggressive spreader.
I hadn't considered L. punctata. I think gardengal has it right, it doesn't have flowering branches like L. vulgaris.