When running this little program, 0 for a sales amount should always deliver the error message. For some reason after I enter some other incorrect values and then try 0, the program allows it and completes. Must be something with the loop but I can't tell. Do I need to group the 2 "while"s together or what? Help please 
Code:
#Define the main function
def main():
# create a variable to control the loop
keep_going = 'y'
# create a counter for salesperson's
number_of_salespersons = 0
# process each salesperson's sales
while keep_going == 'y' or keep_going == 'Y':
# use a function to process each salesperson
process_salesperson()
number_of_salespersons += 1
# are there more salesperson's?
keep_going = raw_input('Are there more salespeople? (enter y for yes): ')
# display the total number of salespeople
print "There were", number_of_salespersons, "salesperson's."
def process_salesperson():
# get the salesperson's name
name = raw_input("What is the salesperson's name? ")
# input the first sale amount
print 'Enter', name + "'s first sale amount:",
first_sale_amount = input()
# validate the sale amount is > $1 and < $25000
while first_sale_amount < 1:
print "ERROR: the sale amount must be between $1 and $25000."
first_sale_amount = input("Please enter a correct sale amount: ")
while first_sale_amount > 25000:
print "ERROR: the sale amount must be between $1 and $25000."
first_sale_amount = input("Please enter a correct sale amount: ")
# intialize average, highest, and lowest sale amount
total_sales = first_sale_amount
highest_sale = first_sale_amount
lowest_sale = first_sale_amount
# get the number of sales for this person
print 'How many sales did', name, 'have?',
number_of_sales = input()
for number in range(2, number_of_sales + 1):
# get the sale amount
print 'Enter', name + "'s amount for sale #" + str(number) + ':',
sale_amount = input()
# validate the sale amount is > $1 and < $25000
while sale_amount < 1:
print "ERROR: the sale amount must be between $1 and $25000."
sale_amount = input("Please enter a correct sale amount: ")
while sale_amount > 25000:
print "ERROR: the sale amount must be between $1 and $25000."
sale_amount = input("Please enter a correct sale amount: ")
# accumulate the sales
total_sales += sale_amount
# check for highest sale
if sale_amount > highest_sale:
highest_sale = sale_amount
# check for lowest sale
elif sale_amount < lowest_sale:
lowest_sale = sale_amount
# compute average sale
average_sale = float(total_sales) / number_of_sales
# display the average, highest, and lowest sales
print
print name + "'s average sale was: \t $%6.2f" % average_sale
print name + "'s highest sale was: \t $%6.2f" % highest_sale
print name + "'s lowest sale was: \t $%6.2f" % lowest_sale
print
# call the main function
main()