Are you not able to work through the data using prior tax filing(s)?

Taking depreciation is not an option.

Get all prior tax returns/transcripts, and you can often figure out the prior depreciation.

Even getting SOME of prior information (tax returns/transcripts) can help you figure out what was done before.  And unless evidence shows otherwise, assume that prior depreciation is correct.

https://www.irs.gov/newsroom/heres-how-people-can-request-a-copy-of-their-previous-tax-return

If an item is depreciable you depreciate it.

It is not a choice for you or the client.

Upon sale you get dinged for the larger of depreciation allowed or allowable.

Have client do some more digging and/or request from prior preparer.

That has got to be a new record - three answers posted in under one minute of each other.  Hopefully Intuit still has the podiums setup to award the gold, silver, and bronze for this one.

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@IRonMaN wrote:

Hopefully Intuit still has the podiums setup to award the gold, silver, and bronze for this one.

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I shouldn't have done the link ... that lost me the gold and dropped me to silver.

😂

At some point, it must be reckoned with. I would use a computational method to recreate the accumulated depreciation that SHOULD have been taken. I found  https://www.calculator.net/depreciation-calculator.html which can be useful in doing this. 

Give the client the option - pay you to do it right, or have you do it in a manner that shows all assets fully depreciated (not a good choice). Explain the cost difference in doing both. Third option - you can both go your own way and say "It's been nice meeting you."