Use the columns monthly_spend_k, transactions, avg_balance_k and online_pct, scaled with StandardScaler (call the result X). Fit KMeans(n_clusters=4, n_init=10, random_state=0) on X.
For every customer, find the distance (in scaled units) to the centre of their own group. Store the customer_id with the biggest distance in result. Unusual customers are worth a closer look.
import io
import pandas as pd
cards = pd.read_csv(io.StringIO("""customer_id,monthly_spend_k,transactions,avg_balance_k,online_pct
701,42.9,59,173,69
702,26.6,29,12,54
703,50.7,56,166,78
704,19.1,19,17,41
705,6.7,10,38,8
706,15.3,34,9,53
707,108.3,28,487,29
708,53.8,51,178,74
709,18.9,39,12,45
710,87.9,36,353,44
711,46,65,120,72
712,77.4,32,483,43
713,32.3,52,179,75
714,18.2,33,13,41
715,90.5,28,387,26
716,55.1,55,151,57
717,24.7,37,11,70
718,10.6,18,34,23
719,101.9,16,453,25
720,29.2,49,180,71
721,17.9,33,9,42
722,7.8,11,34,22
723,33.5,64,154,84
724,9.8,15,27,37
725,16.9,25,26,44
726,97.9,20,319,42
727,6.8,13,51,14
728,20.3,27,13,42
729,10.3,16,34,16
730,32.8,53,126,81
731,8.1,11,33,29
732,27.3,23,12,42
733,45.1,52,81,70
734,19.1,35,12,64
735,52,55,148,76
736,54.9,52,135,78
737,7.2,12,53,17
738,10.3,12,53,23
739,15.2,28,19,44
740,47.9,63,128,75
741,84,18,354,25
742,7.5,10,45,26
743,8.7,13,62,38
744,75.6,26,413,53
745,19.5,28,19,48
746,43,44,134,81
747,18,39,14,48
748,12,4,52,15
749,16.6,27,15,56
750,5.4,13,52,26
751,81.9,23,427,29
752,9.1,12,56,15
753,20.8,28,21,45
754,49.3,55,150,73
755,103.5,21,409,24
756,8.9,11,31,15
757,16.9,33,17,38
758,17.5,28,29,26
759,14.1,25,20,35
760,83.1,34,342,47
761,19.7,37,11,31
762,24.1,38,12,41
763,21.2,41,21,39
764,22.6,31,17,45
765,46.5,55,117,67
766,56.2,55,180,84
767,7.7,9,40,30
768,9.1,15,45,5
769,43.7,53,186,67
770,22,37,15,52
771,8.1,10,41,24
772,10,8,38,20
773,17.8,30,9,45
774,6,8,38,9
775,46.8,56,159,68
776,22.5,31,11,43
777,90.3,23,429,37
778,8.4,17,20,33
779,26.9,31,13,39
780,40.6,50,185,71
781,33.2,46,125,84
782,49.9,47,132,73
783,13.5,26,20,49
784,60.9,33,135,86
785,45.3,45,184,79
786,105.3,19,466,33
787,7.7,12,32,36
788,21.1,32,20,32
789,14.2,26,0,20
790,55.4,31,451,23
791,17.2,29,5,39
792,22.3,20,15,56
793,26.8,28,4,40
794,95.5,32,378,51
795,93.6,27,485,20
796,109.6,12,432,45
797,45.3,43,156,77
798,7.8,9,39,20
799,43.2,51,114,87
800,7.3,11,29,15
801,20.8,28,16,37
802,49,47,159,86
803,25.8,31,20,49
804,10.3,14,44,14
805,45.8,52,161,79
806,20.2,32,14,23
807,50.4,48,195,68
808,20.3,22,13,44
809,93.1,29,372,11
810,47.9,52,200,67
811,86.3,23,416,52
812,43.4,54,135,78
813,9.7,10,53,26
814,39.3,58,210,86
815,10.3,14,54,15
816,89.8,26,351,31
817,5.4,20,32,20
818,14.1,34,13,50
819,10.9,12,38,36
820,86.1,19,372,36
821,100.4,26,453,37
822,38.6,57,118,68
823,8.8,15,45,23
824,9,10,37,28
825,18.6,26,16,40
826,39.2,52,127,92
827,67.6,21,462,28
828,7.6,7,54,18
829,81.9,25,440,33
830,23.3,19,21,23
831,21.4,23,13,47
832,20.2,32,20,56
833,86.7,32,509,15
834,7.2,8,48,22
835,12.4,11,30,36
836,16.4,39,19,69
837,54.3,59,152,68
838,39.8,40,174,85
839,10.1,11,37,12
840,4,11,54,23
841,86.4,22,418,32
842,10.2,16,21,19
843,5.9,7,46,36
844,20.5,31,22,38
845,49.1,50,177,76
846,88.4,29,476,10
847,17.3,25,12,53
848,5.9,7,44,16
849,79.6,28,437,16
850,7.3,14,37,18
851,37.5,63,131,81
852,23.4,36,22,52
853,97.4,20,454,38
854,6.8,9,50,7
855,27.7,34,19,51
856,7.2,10,62,26
857,77.3,29,465,22
858,4.2,8,49,15
859,45.1,49,161,69
860,90.2,27,389,13
861,90.3,21,339,21
862,47.7,57,169,77
863,82.4,29,372,36
864,7.6,13,33,14
865,92.5,23,436,30
866,8.8,10,45,14
867,78.6,18,411,35
868,76.3,31,395,35
869,10.7,18,60,28
870,5,13,26,8
871,14.3,36,17,49
872,35.5,57,152,71
873,17.1,28,14,46
874,12.1,13,30,31
875,47.2,50,127,75
876,8.4,13,41,28
877,82,25,381,39
878,18.9,27,20,43
879,44.1,52,180,67
880,15.3,29,12,47
881,47.7,49,145,60
882,81.8,30,290,36
883,12.7,29,2,50
884,22.2,31,19,64
885,8.6,22,41,28
886,17,30,13,47
887,50.4,80,143,63
888,18,31,7,47
889,95.9,25,451,14
890,111.8,19,319,23"""))Store your final answer in a variable named result.
Each hint gives a little more help. Try on your own first.
Run your code to see the output here.