Legal Question in Landlord & Tenant Law in Massachusetts

From a common sense standpoint, I think you are correct to be wary of this request.

That being said, I don't think there is any rule on the timing of an advance first-month, last-month, and security payment. You just want to make sure that you have a written lease in exchange for that kind of money and all proper receipts. The realtor's fee is just another item to be negotiated between you and your landlord, and who pays it might depend on whether you hired the broker to find you an apartment or the landlord hired the broker to find you.

I don't think that a realtor's fee counts toward the total amount that a landlord is legally permitted to request prior in advance, since it doesn't really go to the landlord.