Commercial rental, landlord files individually, does tenant need do Backup Withholding?

My wife and I have a small building in TN which we rent to a dental practice.  We file a joint tax return and do not have a corporation or LLC for the property, it is simply in our name.  The renter's accountant has asked us to send them a W-9 which is easy to do.  However, the W-9 instructions seem to indicate that we do not have an exclusion and therefor the renter should be withholding 24% for "Backup Withholding" as part of their rent payments. Our renters haven't asked for a W-9 before and we've simply charged the full rent which they've paid.  For tax purposes we've shown their rent as income and calculated the federal taxes due at tax time.   

Are doing this wrong?  Should the tenant be withholding taxes?  1) That is counter to what we've done previously; 2) That seems like a high administrative burden to put on renters; and 3) Doesn't make a lot of sense to me.  I'd much rather make estimated quarterly tax payments than have to put that on tenants.

OR ... can I just indicate on the W-9 I'm excluded from Backup Withholding and do things as I have been.

Any guidance appreciated.

Thank you!