I am not encouraging any one to enter on B2 and marry USC but for your information purposes if you are knowledgeable you can get away with it.
Provided you do not have any other negative factors in AOS you can adjust status.
Hopefully it helps
Preconceived Intent and USC Case: If immediate relative, tell the INS officer to read his INS Operations Manual at OI 245.3(b)
"In the absence of other adverse factors, an application for adjustment of status as an immediate relative should generally be granted in the exercise of discretion notwithstanding the fact that the applicant entered the United States as a nonimmigrant with a preconceived intention to remain. Matter of Cavazos, Int. Dec. 2750 (BIA 1980) clarified and reaffirmed. Matter of Ibrahim, Int. Dec. 2866 (BIA 1981)."
The question often arises “May an ‘immediate relative’ of a United States citizen apply for adjustment of status shortly after arriving in the United States?” The answer is yes. This matter has been considered by the Board of Immigration Appeals and resolved in favor of applicants.
BIA decisions are, by law, binding upon all CIS officers. In an important precedent decision, Matter of Cavazos, 17 I&N Dec. 216 (BIA 1980), the Board of Immigration Appeals reviewed a matter in which an application for adjustment of status had been denied because of “pre-conceived intent.” In that case, the applicant entered the United States and, that same day, married a United States citizen. He was put into deportation proceedings as an overstay and he applied for adjustment of status. The immigration judge denied the adjustment application on the basis that the applicant had the pre-conceived intent to immigrate to the United States when he entered as a nonimmigrant. The Board reviewed the facts of the case on appeal and reversed the judge’s holding.
The BIA first noted with approval the policy of the former INS to waive this basis for denial in the absence of any other negative factors. The Board held:
“We believe, however, that the policy manifest in the Instruction, i.e., to favor immediate relatives seeking a grant of adjustment of status by essentially negating preconceived intent as an adverse factor in meritorious cases , may appropriately be adopted by the immigration judge and the Board in exercising discretion on applications for relief under section 245.
The finding of preconceived intent was the only negative factor cited by the immigration judge in denying the respondent’s adjustment application and no additional adverse matters are apparent in the record. A significant equity is presented by the respondent’s United States citizen wife and child. We conclude that a grant of adjustment of status is warranted in this case and will sustain the appeal . . .”
Subsequently, this holding has been cited with approval by the BIA in similar cases.
Essentially, in the absence of any serious negative factors, this holding stands for the proposition that “preconceived intent” is a legally insufficient reason to deny adjustment of status to an immediate relative of a US citizen.