And what does your attorney say if you use one.
Without the estoppel, you only got the seller side of the story, and have to assume the seller and his tenant abide assiduously by the lease. One of the things mentioned in the estoppels that our attorney sends out is the rents are all paid up to date, and the deposits paid is what is stated on the lease, with no notification of anything deducted from it.
Once the tenant confirm the terms and amounts, then there can be no argument when you take over from the tenant saying that the prior owner deviated from the lease in this that or the other way.
If an agent said that, then I wonder what the seller is trying to hide. Maybe it's nothing, but as they say, you don't know what you don't know.
I agree, the Estoppel agreements protect you and the tenants. They simply confirm what the lease says. They should be a one-page document that's easy for the tenants to sign and agree.
With the number of documents you'll need to sign and handle for a typical closing, another couple to confirm rent/deposit/etc, seems well worth the effort of everyone involved.
If it were me, I would require tenants to complete them prior to closing. Any discrepancies need to be coordinated between you and the seller.
Are estopels common in the market you are buying in? They are not in all markets.
Depending on the size of the place in my area they are not common. Especially when they are value add deals. Lucky to a ziplock bag full of unlabeled keys.