A buy box is specific enough when someone else could use it without asking you a single follow-up question. "SFH, under 200k, decent areas" fails that test three ways: you don't know which streets, you don't know what price means relative to value, and you don't know what condition they'll accept.
A usable version reads more like: single family, 3 bed 1.5 bath minimum, 1,000 square feet or more, built 1955 or later, these six zip codes and not the school district on the west side, purchase price at or below 75 percent of after repair value minus my repair estimate, will take cosmetic and mechanical work, will not take foundation or fire damage, pays cash, closes in 14 days, wants to see the property before signing.
The way you get that out of a buyer is by asking about the past rather than the future. What did you buy last, what did you pay, what did you put into it, what did it appraise or sell for. People describe their ideal in vague terms and describe their actual purchases precisely.
The other half of your problem may not be vagueness. If buyers say close but no, sometimes what they mean is your repair number is low, so the price only looks like a deal on your math. Ask the two who passed most recently what number they'd have said yes at, and compare it to what you offered. If their number is consistently 15 to 20 percent below yours on repairs, that's an estimating gap, and no amount of buy box detail fixes it.