They just do not believe your marriage is real. Think about your first interview honestly and realistically. What went wrong? You may think everything was fine. Relax, If you are truly in a real marriage, and not just trying to gain an immigration benefit, you will survive this. If not, you will not fool USCIS. They hold all the cards. Don't even try. How well do you know your spouse? At your first interview, were you nervous? Did you say something that would lead the immigraion examiner to doubt your marriage? It is more common that expected that a nervous person cannot remember their anniversary date or even thier own birthday. You need to be calm when you are called back. Do you or your spouse have a terrible memory? You may need a doctor's note explaining you have memory or medical issues that cause forgetfulness.
Do we have documentation of our relationship?
Bringing a marriage certificate only proves you went through a ceremony, not that you live together. You need documentary evidence of your relationship: photos on many occasions, with and without other people as well as you and your spouse, (not just the marriage day, but everyday photos as well as special occasions) leases, rental agreements and mortgages together, telephone bills, cell phone bills, power bills, signed report cards of stepchildren, food warehouse club memberships together, mail addressed to both of you at the marital address, car, life or health insurance showing each other's names as co-policy holders or beneficiaries and affidavits from friends and relatives who know you as a couple and family unit. These are just examples. Think about your life together and what proves it.
What does the public records check reveal to USCIS?
Are you hiding anything from your spouse? Now is not the time to be secretive. Previous marriages, debts, criminal matters all show up in the public records search that USCIS performs before you step into the room. Remember you are going to be interviewed separately and if you asked about things your spouse may not have told you, they will conclude you do not have a real marriage. Example: A spouse who does not want his spouse to know he had a previous marriage because divorce is forbidden in his religion. It will come out. USCIS has your complete criminal record, driving record and credit report. They know where you have lived. They know if your name is also on a lease with your brother or former significant other and will assume you live at the other address so take your name off any old leases with prior roommates. Do your driver licenses or state IDs show the same address? Why not? FIx it now.
Why are we interviewed separately?
Each spouse will be asked the same questions and the answers compared. It will be videotaped. They are looking for disparate answers so if you do not know an answer, do not guess. Explain why you do not know if needed. They may try to talk the US citizen into withdrawing the case, threatening him/her with fines and imprisonment. Since your marriage is real, do not withdraw the case. Of course you have taken a competent immigration attorney with you to explain the techniques the examiners use
What kinds of questions can we expect?
They will ask 100-150 questions. Examples are Personal - such as Which side of the bed do you sleep on? Where does she keep her underwear? What did you have for dinner last night? Who cooked? Who woke up first this morning? What did you give your wife for her birthday last year? How did you celebrate? Her favorite color?
Biographic - What is your husband's Mother's name? When did you last see his Mother? When is your anniversary? How many brothers and sisters does your husband have? What are their names? Where did he live when you first met? Who attended your marriage ceremony at the courthouse?
Household- Gas or electric cooking? How much is your mortgage or rent? Do you have a microwave. Name the electronics in your bedroom. How many floors, bedrooms, baths in your home? How much is your spouse's salary? Are they paid weekly or biweekly? Where do you grocery shop?
What happens next
You will either get an approval or intent to deny letter. Rarely, you will get a request for additional documents. If you do not respond to the intent to deny with reasonable explanations of disparate answers, you will be denied and placed in removal proceedings. Appeals to the Board of Immigration Appeals are possible but are beyond the scope of this guide.
Do not engage in a "green card marriage". It is wrong on many grounds. Tragically, if you enter into a fraudulent marriage (even if you later withdraw the filing) and later on enter into a real one, you will be precluding from gaining an immigration benefit on the second relationship except under the most exceptional circumstances.