Your toilet is loose!
We hear this from home inspectors who are trained to straddle the toilet and try to move the bowl from side to side.
Frequently the bowl is a bit loose and the inspector writes this in the report as defective. The buyer then requests the seller to do this tightening.
Suggest that the buyer do the tightening or have someone do it for them. Be careful if you are the one to tighten the 2 bolts on the floor. One tiny partial turn and you have a cracked porcelain bowl. This cannot not be fixed ...the entire toilet must be replaced.
Please let the buyer or buyer's contractor do the tightning.
Do not do it yourself !