Closing costs - depends on the offer. It is about 1% of the purchase price and includes various state and federal registration, mortgage, title, and other fees, attorney's fees, pre-paid items (like taxes or condo fees, water/sewer, etc), and other miscellaneous costs of completing the transaction.
Typically, the buyer pays these. However, in the last few months I see more and more transactions where the initial offer asks for the seller to contribute so that the buyer can put more of that cash into down payment instead.
Let me know if you need help with your transaction! Waltham is a specialty!