How troublesome/costly is it in MA to get a judgement for unpaid rent in small claims court and then use it to garnish the defendent's wages? Will I need a lawyer for the latter? Will the costs exceed the benefits?
Also, will either of these affect their credit rating if I do not have their social security number?
Any court judgement for back rent or payment owed will affect the tenants credit report. Just make sure you watch your own credit report. My judgment accidentally went to my credit report and it took me 2 months to get them to remove it from mine and apply it to my ex-tenant.
If you can prove the tenant is working, you should be able to garnish wages. If you can't, don't expect to ever get any of the back money. Tenants who don't pay now will most likely never pay without being forced.