When Beckett and Castle find the rug in the storage unit, a close up shot of the rug shows it snug against the wall. Shots from farther away show it moved away from the wall enough for Kate to walk next to it to unroll it.
Beckett refers to a situation where an IRS auditor is paid to act as someone's tax consultant as a "legitimate arrangement". While not illegal, it's not legitimate, either. Employees of the IRS are prohibited from receiving money or anything of material value for tax advice or preparation. It's a violation of professional ethics.