Great question to ask. I've been in that dilemma a lot myself. I most relate to @Joel Owens answer, and I'd add these points:
What are your objectives? If it's to sell, you might go for more TI and higher rents, after considering everything else
In any case, I concur with the remarks emphasizing tenant credit quality.
- How much of the expense will create additional rental dollars with a different tenant in the future? E.g. putting in two bathrooms, a grease trap, a vent hood and so forth in an area with a short supply of second generation restaurants could result in higher rents with another tenant than you'd otherwise forecast
- How much skin are they putting in? If they're doing a 250k finish out, and they're proposing I pay for all of it, that's a tall order (but might do for a national corporate lease). If they are putting in 175k and I'm putting in 40k, and a lot of both of those amounts go to improving the building under the point above, that makes more sense to me
- To the extent that the costs do *not* add additional rent dollars in your pocket as I mention above, then you've got to evaluate your risk. I generally start my forecast assuming that 90% + restaurants will fail within a few years.
- Generally, this is just me, but because I'm not planning to sell my retail investments soon, if I think it is a great local tenant who is making some solid marketable improvements to the space eg. ADA bathrooms, killer outdoor seating areas, I could see abating rent in lieu of their TI allowance as someone mentioned. but am very careful in how I do that so that it is conditioned on their well defined improvements. I use a good lawyer to draft lease provisions on that.