should we gamble $1000 to wait for appraisal or walk away? plea

We signed the cotract for purchase of a commercial residential mixed property for $400k , it is fully rented for $3100 /month, renovated 6 years ago. except some defects, it is in good condition.  1st floor has 5 year lease. We just found that the property next door is sold for $320k on August, the deed is record recently, and we could not see the record until yesterday.  the buyer agent for that property said the buyer will spend $40k to update the property, and 2nd , 3rd floor are rent for 1800/total. the first floor is not rented yet.   the recent sales on this commercial street are less than 400k right now. highest is $395k.  We paid $520 inspection fee, may be able to withdraw the $1000 deposit for apprasal.   the lender said that if appraisal come out lower than $400k, then we can bargain the price with Seller again since we can not get the loan.  that will be ideal situation.  We spend a lot of time to fnd this property, and it can generate nearly $1000 cash flow /month.  but we  don't like to overpay the property either . how likely that the appraisal will come out lower than 400k?

Thanks for your opinion