Pre-LOI Balance Sheet Review - What (specifically) to look for?

Hello, first post from a first time searcher! Hopefully I can add enough context to the title to solicit specific feedback. I have read the books, spent countless hours listening to the podcasts, am generating deal flow, etc., and I think I found a quality business that checks out running numerous scenarios in the SMBootcamp financial model template, having several conversations with the owner about the business, posing numerous questions, and reading the reviews on the company etc.

My question is: I just received full access to the tax filings, P&L, and balance sheets for the last 3 years, and other than reviewing the basics, following the numbers at a high level to ensure a consistent story is being told, inputting the returns into the model and comparing that vs. the financials provided in the CIM, and noting any outliers or items that stand out to follow up on in diligence, what specifically should I be looking for, particularly on the balance sheet, to get answered prior to submitting an LOI?

I suppose another way to ask is what are your best red or yellow flag filters, specific things to look for, etc., that are appropriate to diligence prior to LOI and the formal due diligence period?

I don't want to get too bogged down now and have another offer come along, but also don't want to get too far down a deal path and have to do a lot of right sizing later if there are quick screens, filters, sniff tests I can do now. Thanks in advance for any tips and pointers!