Of course you want to be paid, and not be considered mean. there are businesses who take advantage of someone being too nice.
I learned this lesson the hard way as well. I ended up not getting paid on several accounts, and then I decided to follow what all the big businesses do. In the agreement that we discuss before any work is started my new client understands that a retainer is required and the final protion of the job will not be released until the final balance is paid. The final passwords are not released until everything is paid. I did have prospective clients balk at this portion of the agreement, and I learned through the grapevine, they didn't pay the person they went with.
To collect on unpaid invoices, I still do what big businesses do. I researched and found formal collection letters that are still nice, but firm. The letters advise the time schedule for paying the invoice, the time limit before it goes to collection. Only one client failed to every pay and they went out of business.
Good luck