Look, I have no idea what your problem is but someone saying they're on a budget does not make them dodgy and likely to run off without paying. Very odd thing to say to someone in my opinion. The warning signs are not there, you are just seeing something does doesn't exist.
The reason that saying that rings alarm bells is that the job is what it is and it costs what it costs.
When people say they are on a budget, nobody thinks that they are (especially) likely to run off without paying but what people do do is make their problems yours.
Gosh that's a lot. Is there any way we can get that down a bit? I was hoping you'd finished by now. Ah, the (cheapest) sparky has let me down. Job will be ready tomorrow.
I'll labour on you (no you f**k**g won't)
I'll board it (don't you f**k**g dare)
Listen, I'm just waiting for that cheque to clear, can you hang on a day or two.